Lone DNC Hacker Guccifer 2.0 is linked to the GRU, the Russian military intelligence agency
24.3.2018 securityaffairs BigBrothers
The US investigators concluded that the Russia-linked hacker Guccifer 2.0 is directly tied to the GRU, the Russian military intelligence agency.
Guccifer 2.0 is the alleged hacker behind the DNC hack that also released a huge trove of documents about House Democrats, including Nancy Pelosi’s sensitive data.
In February 2016, researchers from security company CrowdStrike, pointed out that the DNC attack wasn’t the result of the action of a lone wolf, instead, two sophisticated Russian espionage groups, COZY BEAR and FANCY BEAR were involved in the cyber espionage operation.
A portion of the intelligence community believes that the Russia-linked hacker Guccifer 2.0 is a Russian intelligence agent.
This week, The Daily Beast published a report that confirms that Guccifer 2.0 is linked to the GRU, Russia’s military intelligence agency.
“Guccifer 2.0, the “lone hacker” who took credit for providing WikiLeaks with stolen emails from the Democratic National Committee, was in fact an officer of Russia’s military intelligence directorate (GRU), The Daily Beast has learned.” reads the analysis published by The Daily Beast.
“It’s an attribution that resulted from a fleeting but critical slip-up in GRU tradecraft.”
In January 2017, the US intelligence linked the the DNC hack and the cyber attacks against the Hillary Clinton’s campaign to Russian intelligence groups.
Guccifer 2.0 took credit for some of the attacks denying any link with the Kremlin, by US authorities believe the hacker is a product of a Russian disinformation campaign.
The experts at cybersecurity firm ThreatConnect also determined that Guccifer 2.0 was linked to Russian intelligence. According to ThreatConnect, Guccifer 2.0 had been using a Virtual Private Network service, Elite VPN, to remain anonymous, but on one occasion he failed to activate the VPN client before logging on.
According to a source familiar with the government’s Guccifer investigation, the hacker was using a system having a Moscow-based IP address that was logged by an American social media company.
“Almost immediately various cyber security companies and individuals were skeptical of Guccifer 2.0 and the backstory that he had generated for himself,” said Kyle Ehmke, an intelligence researcher at the cyber security firm ThreatConnect. “We started seeing these inconsistencies that led back to the idea that he was created hastily… by the individual or individuals that affected the DNC compromise.”
“Working off the IP address, U.S. investigators identified Guccifer 2.0 as a particular GRU officer working out of the agency’s headquarters on Grizodubovoy Street in Moscow. (The Daily Beast’s sources did not disclose which particular officer worked as Guccifer.)” continues the report.
The GRU military agency is believed to run the dreaded Fancy Bear APT, that is behind the DNC hack, cyber espionage campaign against NATO and Obama’s White House and cyber attacks against the World Anti-Doping Agency, and numerous militaries and government agencies in Europe, Central Asia, and the Caucasus.
The special counsel Robert Mueller determined that Russia intelligence interfered with US elections in the attempt to boost Trump’s candidacy.
On July 22, 2016, WikiLeaks began releasing the documents stolen by Guccifer 2.0, a huge trove of approximately 19,000 emails and 8,000 attachments stolen by the hacker. Trump promptly promoted the leak on Twitter, while his adviser Roger Stone in an article written for Breitbart (a name familiar with Cambridge Analytica case too), sustained that Guccifer 2.0 was a Romanian hacktivist.
“Sometime after its hasty launch, the Guccifer persona was handed off to a more experienced GRU officer, according to a source familiar with the matter. The timing of that handoff is unclear, but Guccifer 2.0’s last blog post, from Jan. 12, 2017, evinced a far greater command of English than the persona’s earlier efforts.” concluded The Daily Beast.
“It’s obvious that the intelligence agencies are deliberately falsifying evidence,” the post read. “In my opinion, they’re playing into the hands of the Democrats who are trying to blame foreign actors for their failure.”
Ransomware Hits City of Atlanta
23.3.2018 securityweek Ransomware
A ransomware attack -- possibly a variant of SamSam -- has affected some customer-facing applications and some internal services at the City of Atlanta. The FBI and incident response teams from Microsoft and Cisco are investigating. The city's police department, water services and airport are not affected.
The attack was detected early on Thursday morning. By mid-day the city had posted an outage alert to Twitter. In a press conference held Thursday afternoon, mayor Keisha Bottoms announced that the breach had been ransomware. She gave no details of the ransomware demands, but noticeably declined to say whether the ransom would be payed or refused.
Bottoms could not at this stage confirm whether personal details had also been stolen in the same breach, but suggested that customers and staff should monitor their credit accounts. Questions on the viability of data backups and the state of system patches were not clearly answered; but it was stressed that the city had adopted a 'cloud first' policy going forwards specifically to improve security and mitigate against future ransomware attacks.
A city employee obtained and sent a screenshot of the ransom note to local radio station 11Alive. The screenshot shows a bitcoin demand for $6,800 per system, or $51,000 to unlock all systems. It is suggested that the ransom note is similar to ones used by the SamSam strain of ransomware. Steve Ragan subsequently tweeted, "1 local, 2 remote sources are telling me City of Atlanta was hit by SamSam. The wallet where the ransom is to be sent (if they pay) has collected $590,000 since Jan 27."
SamSam ransomware infected two healthcare organizations earlier this year. SamSam is not normally introduced via a phishing attack, but rather following a pre-existing breach. This could explain the concern over data theft on top of the data encryption. It also raises the question over whether the initial breach was due to a security failure, an unpatched system, or via a third-party supplier.
Ransomware is not a new threat, and there are mitigations -- but it continues to cause havoc. Official advice is, wherever at all possible, refuse to pay. The theory is if the attackers cease getting a return on their attacks, they will turn to something easier with a better ROI on their time. This approach simply isn't working.
Sometimes payment can be avoided by recovering data from backups. But this isn't always possible with SamSam. In the Hancock Health SamSam incident earlier this year, the organization decided to pay the ransom "to expedite our return to full operations", despite having backups. In the event, the SamSam attackers had already closed this route. "Several days later," announced CEO Steve Long, "it was learned that, though the electronic medical record backup files had not been touched, the core components of the backup files from all other systems had been purposefully and permanently corrupted by the hackers."
It isn't yet known whether the City of Atlanta attack is definitely a SamSam attack, whether the system was breached prior to file encryption, nor whether backup files have been corrupted. These details should become clear over time. The fact that Hancock Health decided to pay the ransom, and had its systems back up and running within days, may become part of Atlanta's decision on whether to pay or not.
Apart from recovering from backups or paying the ransom, the only other option (assuming that there are no decryptors available from the NoMoreRansom project) is to stop the encryption the moment it starts. Traditional anti-malware perimeter detection will not stop modern malware. That means prevention requires very rapid and early detection.
"Ransomware spreads like wild fire, and is the most time critical of cyber threats," comments Matt Walmsley, EMEA Director at Vectra. "The ability to detect the pre-cursor behaviors of ransomware is the only way to get ahead of the attack. Unfortunately, that's almost impossible to do using traditional manual threat hunting techniques. That's why forward-thinking enterprises are increasingly using an automated approach, using AI-powered threat detection. You need to detect and respond at machine speed."
Timely patching is also vital, especially where the attacker breaches the system prior to encryption. "When you are told to patch months before and witness precursor warnings like WannaCry and NotPetya going by," exhorts Yonathan Klijnsma, threat researcher at RiskIQ, "well, you damn well better patch. If your organization's patch management is so problematic that it takes this long, you have to change it. Events of this potential magnitude and impact require management to respond by elevating maintenance and patching to mission critical status until they are resolved. The ROI is clear, consider the costs and material loss of your company going down for a day, versus shifting priorities to give your engineers more time to manage patches properly. It's not a good time to roll the dice."
Connected cities are becoming increasingly like large corporations. "A city has some hallmark characteristics of a large enterprise," suggests Rapid7's chief data scientist, Bob Rudis: "there are a large number of employees and contractors with a diverse array of operating systems, hardware and data types that all need protection. Beyond financial account information and general personally identifiable information (PII), city-related systems and networks can and do contain court and criminal records, tax records, non-public information on police and other protective services employees, department activities/plans and more. Much of this is extremely sensitive data and would be treasure trove of information, capable of being used in a diverse array of disruptive, targeted attacks against both individuals and entire departments."
What all this means is anti-ransomware preparations require at least three layers of defense: off-site backups; an efficient patch regime; and real-time anomaly detection. Relying on IT staff 'noticing something peculiar' (as happened with the City of Atlanta) is simply not good enough.
TrickBot Gets Computer Locking Capabilities
23.3.2018 securityweek BotNet
A recently observed variant of the TrickBot banking Trojan has added a new module that can lock a victim’s computer for extortion purposes, Webroot reports.
First observed in late 2016 and said to be the work of cybercriminals behind the notorious Dyre Trojan, TrickBot has seen numerous updates that expanded not only its capabilities, but also its target list.
Last year, the malware received an update that added worm-like capabilities, allowing it to spread locally via Server Message Block (SMB).
Webroot now says that the malware attempts to leverage NSA-linked exploits released by Shadow Brokers last year in order to move laterally within compromised networks.
The new TrickBot variant installs itself into the %APPDATA%\TeamViewer\ directory, and once up and running, creates a “Modules” folder to store encrypted plug and play modules and configuration files.
While many of the modules have been already documented, the new Trojan variant also includes a module internally called spreader_x86.dll that Webroot hasn’t seen before. Featuring a large rdata section that contains two additional files, the spreader module contains an executable called SsExecutor_x86.exe and an additional module named screenLocker_x86.dll.
Spreader_x86.dll, the security researchers have discovered, was clearly designed to allow the malware to spread laterally through an infected network by leveraging the NSA-linked exploits.
“This module appears to make use of lateral movement in an attempt to set up the embedded executable as a service on the exploited system. Additionally, the TrickBot authors appear to be still developing this module as parts of the modules reflective dll injection mechanism are stolen from GitHub,” Webroot notes.
The SsExecutor_x86.exe part of the new module is meant to be executed after exploitation, to achieve persistence by modifying registry to add a link to the copied binary to the start-up path of each user account.
Written in Delphi, ScreenLocker_x86.dll represents TrickBot’s first ever attempt at “locking” the victim’s machine. The module exports two functions: a reflective DLL loading function and MyFunction, which appears to be the work in progress.
Should TrickBot indeed gain the locking functionality, it would mean that its developers have decided to switch to a new business model, similar to that employed by ransomware operators.
Locking the computer before stealing the victim’s banking credentials would prevent the credit card or bank theft, which suggests that the cybercriminals might be planning to extort victims to unlock their computers.
The security researchers suggest that, in corporate networks where users are unlikely to be regularly visiting targeted banking URLs, TrickBot would find it difficult to steal banking credentials. Thus, the potential of locking hundreds of machines could prove a more successful money-making model.
“It is notable that this locking functionality is only deployed after lateral movement, meaning that it would be used to primarily target unpatched corporate networks. In a corporate setting (with unpatched machines) it is highly likely that backups would not exist as well. The authors appear to be getting to know their target audience and how to best extract money from them,” Webroot points out.
U.S. Imposes Sanctions on Iranians for Hacking
23.3.2018 securityweek BigBrothers
U.S. Charges Iranians in Massive Hacking Scheme
The United States unveiled charges on Friday against nine Iranians for their alleged involvement in a massive state-sponsored hacking scheme which targeted hundreds of universities in the US and abroad and stole "valuable intellectual property and data."
Ten Iranians were also hit with sanctions along with an Iranian company, the Mabna Institute, which engaged in computer hacking on behalf of Iran's Revolutionary Guards, the US Treasury Department said.
The two founders of the Mabna Institute, Gholamreza Rafatnejad, 38, and Ehsan Mohammadi, 37, were among the nine Iranians indicted in New York and whose assets are subject to US seizure.
Since 2013, the Mabna Institute carried out cyber intrusions into the computer systems of 144 US universities, the Treasury Department said, and 176 universities in 21 foreign countries.
Mabna Institute employees and contractors "engaged in the theft of valuable intellectual property and data from hundreds of US and third-country universities... for private financial gain," it said.
"For many of these intrusions, the defendants acted at the behest of the Iranian government and, specifically, the Iranian Revolutionary Guard Corps," Deputy Attorney General Rod Rosenstein said.
The US Department of Labor, the US Federal Energy Regulatory Commission, dozens of private firms and non-governmental organizations such as the United Nations Children's Fund were also allegedly targeted.
Geoffrey Berman, US Attorney for the Southern District of New York, said the Iranians conducted spearphishing attacks designed to steal passwords from email accounts in one of the "largest state-sponsored" hacking schemes ever uncovered.
- 8,000 accounts compromised -
The email accounts of more than 100,000 university professors worldwide were targeted, Berman said, and about 8,000 accounts were compromised.
He said 31 terabytes -- about 15 billion pages -- of academic data and intellectual property were stolen.
This included "research, and other academic data and documents, including, among other things, academic journals, theses, dissertations, and electronic books," the Justice Department said.
"The defendants targeted data across all fields of research and academic disciplines, including science and technology, engineering, social sciences, medical, and other professional fields," it said.
David Bowdich, deputy director of the FBI, said the defendants are in Iran and "apprehending these individuals presents a challenge."
"(But) the long arm of the law reaches worldwide," he said. "You cannot hide behind a keyboard half way around the world and expect not to be held to account," Berman said.
One of the 10 Iranians subject to sanctions, Behzad Mesri, was already indicted in November 2017 in connection with the theft of scripts and plot summaries for HBO's "Game of Thrones," and for trying to extort $6 million in Bitcoin out of the network.
The Justice Department said that besides targeting university professors in the United States, the hackers also compromised accounts in Australia, Canada, China, Denmark, Finland, Germany, Ireland, Israel, Italy, Japan, Malaysia, Netherlands, Norway, Poland, Singapore, South Korea, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Rafatnejad, Mohammadi and the seven other Mabna Institute employees or contractors were charged with identity theft, conspiracy to commit computer intrusions and other crimes.
Facebook as an Election Weapon, From Obama to Trump
23.3.2018 securityweek Social
The use of Facebook data to target voters has triggered global outrage with the Cambridge Analytica scandal. But the concept is nothing new: Barack Obama made extensive use of the social network in 2008 and stepped up "micro-targeting" in his 2012 re-election effort.
The unauthorized gathering of data on 50 million Facebook users by a British consulting firm that worked for Donald Trump has sparked intense debate on how politicians and marketers -- appropriately or not -- use such personal information.
But Cambridge Analytica, the firm at the center of the firestorm, has stressed it is far from alone in using data gleaned online to precisely target voters.
"Obama's 2008 campaign was famously data-driven, pioneered micro-targeting in 2012, talking to people specifically based on the issues they care about," the British firm said on Twitter.
Former members of the Obama team fiercely dispute any comparison to the Cambridge Analytica case, in which an academic researcher is accused of scooping up a massive trove of data without consent using a Facebook personality quiz, and transferring it improperly to the firm.
"How dare you!" tweeted Michael Simon, who headed Obama's micro-targeting team in 2008, in response to the firm.
"We didn't steal private Facebook profile data from voters under false pretenses. OFA (Obama's campaign) voluntarily solicited opinions of hundreds of thousands of voters. We didn't commit theft to do our groundbreaking work."
Jeremy Bird, a member of the 2012 Obama team, echoed those sentiments, warning: "Do not use the Obama campaign to justify your shady business."
But while Cambridge Analytica's methods for acquiring data are in dispute, the underlying goal -- using social media to take the pulse of voters and find those who are persuadable -- was common to both campaigns.
So-called micro-targeting, which borrows techniques from the marketing world, is as much about mobilizing voters and getting them to the polls as about changing minds.
And micro-targeting long pre-dates the internet, with campaigns as early as 1976 using this method, according to Victoria Farrar-Myers, a political scientist and researcher at Southern Methodist University.
Everyone who uses social media makes a decision to share some personal information, she says, although they "may not be fully aware of how people can utilize that."
"Being able to micro-target a voter down to what magazine they read and what issues might make them turn out does have an advantage for a candidate when they're running for an election."
"The Trump campaign did quite a good job at micro-targeting," she said, noting that it put a heavy focus on seemingly marginal localities that were identified as potentially winnable thanks to socal media, and ended up tipping Republican.
According to documents released by the Federal Election Commission (FEC), Trump's new choice of national security advisor John Bolton also hired Cambridge Analytica to conduct profiling work for his Super PAC fundraising group in support of Republican congressional candidates.
Waking up to problem
What remains unclear is whether the techniques made a difference in the 2016 US election.
Chirag Shah, a Rutgers University professor of information and computer science, said the data gleaned could have been instrumental to Trump's campaign.
"We know from other applications, not just in the political domain, but also all kinds of marketing commercialization domains that these things are very, very instrumental," Shah said.
"It is however speculative to say this really change the outcome of the election. All we can say is that, yes there were people who were influenced or targeted using this data."
Experts also stress that neither the Obama nor the Trump campaign broke any laws on the protection of private data -- or even Facebook's internal rules -- which were tightened in 2015 to prevent developers from collecting people's data without explicit consent.
Shah noted the concerns about improper use of personal data are not new.
"The problem is once people access the data from Facebook, for which they often pay, that data is out of Facebook's hands and out of Facebook's users hands.
"And there's no way that Facebook will be able to track all of the data being shared by third parties, fourth parties."
Rayid Ghani, a University of Chicago researcher who was chief scientist for the 2012 Obama campaign, defended his team's use of Facebook data while arguing for a need for better information that would allow users to know when and how their personal information is collected.
"The public needs to be aware of what data is being collected about them, what it is being used for, who it is shared/sold to, and what they're doing with it," Ghani said in a Medium blog post.
City of Atlanta paralyzed by a ransomware attack, is it SAMSAM?
23.3.2018 securityaffairs Ransomware
Computer systems in the City of Atlanta were infected by ransomware, the cyber attack was confirmed by the City officials.
The city learned of the attack at around 5:40 am local time on Thursday.
On Thursday, Mayor Keisha Lance Bottoms announced on Thursday that a malware has taken in hostage some internal systems, city’s data were encrypted.
City of Atlanta, GA
Mayor @KeishaBottoms holds a press conference regarding the security breach. https://www.pscp.tv/w/bYQLUDEzMzg3MjU2fDFkakdYZFl3YUJQR1p9UR2Gex4Vh6trfD-S2987UbdZclhLRGq6anM2SGyFpQ== …
9:36 PM - Mar 22, 2018
City of Atlanta, GA @Cityofatlanta
Mayor @KeishaBottoms holds a press conference regarding the security breach.
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The ransomware infection has caused the interruption of several city’s online services, including “various internal and customer-facing applications” used to pay bills or access court-related information.
It is still unclear the current extent of the infection, but security experts fear other consequences for the citizens. The mayor recommended the city’s employees and anyone who had conducted transactions with the city to monitor their bank accounts fearing a possible data breach.
“Yesterday morning, computer trouble started interfering with the normal computer operations on the Atlanta government network.” states Forbes.
“Later on, mayor Keisha Lance Bottoms called a press conference to clear the air. The source of the problem: a ransomware attack that had compromised multiple systems.”
“We don’t know the extent so we just ask that you be vigilant,” Bottoms explained in the news conference. “All of us are subject to this attack, if you will. Many of us pay our bills online, we have direct deposit, so go online and check your bank statements.”
Investigators believe that hackers initially compromised a vulnerable server, then the ransomware began spreading to desktop computers throughout the City network. Crooks demanded a payment of 6 Bitcoin, around $51,000 at the current rate,
New Atlanta Chief Operating Officer Richard Cox said that several departments have been affected.
“We don’t know the extent so we just ask that you be vigilant,” Bottoms said in a Thursday news conference. “All of us are subject to this attack, if you will. Many of us pay our bills online, we have direct deposit, so go online and check your bank statements.”
No critical infrastructure and services seem to be affected, the departments responsible for public safety, water, and airport services are operating as normal, however.
Please note our website http://procurement.atlantaga.gov was not affected by this outage and is accessable. https://twitter.com/Cityofatlanta/status/976864741145694208 …
4:08 PM - Mar 23, 2018
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In response to the attack, IT staff sent emails to city employees in multiple departments telling them to disconnect their computers from the network if they notice suspicious activity.
The news media 11Alive.com, cited the opinion of an expert that based on the language used in the message pointed out that the infection was caused by the SAMSAM ransomware.
In February, the SAMSAM Ransomware hit the Colorado DOT, The Department of Transportation Agency and shuts down 2,000 computers.
According to the U.S. Department of Justice, the SAMSAM strain was used to compromise the networks of multiple U.S. victims, including 2016 attacks on healthcare facilities that were running outdated versions of the JBoss content management application.
The SamSam ransomware is an old threat, attacks were observed in 2015 and the list of victims is long, many of them belong to the healthcare industry. The attackers spread the malware by gaining access to a company’s internal networks by brute-forcing RDP connections.
Among the victims of the Samsam Ransomware there is the MedStar non-profit group that manages 10 hospitals in the Baltimore and Washington area. Crooks behind the attack on MedStar requested 45 Bitcoins (about US$18,500) for restoring the encrypted files, but the organization refused to pay the Ransom because it had a backup of the encrypted information.
In April 2016, the FBI issued a confidential urgent “Flash” message to the businesses and organizations about the Samsam Ransomware.
The FBI and Department of Homeland Security are investigating the cyberattack.
The local news channel WXIA published a screenshot of an alleged ransom message, the note demands 0.8 bitcoin (roughly $6,800) per computer or 6 bitcoin ($50,000) for keys to unlock the entire network.
The mayor confirmed that the city would seek guidance from federal authorities on how to “navigate the best course of action”.
GitHub Security Alerts are keeping developers’ code safer
23.3.2018 securityaffairs Security
The code hosting service GitHub confirmed that the introduction of GitHub security alerts in November allowed to obtain a significant reduction of vulnerable code libraries on the platform.
Github alerts warn developers when including certain flawed software libraries in their projects and provide advice on how to address the issue.
The GitHub security alerts feature introduced in November is designed to alert developers when one of their project’s dependencies has known flaws. The Dependency graph and the security alerts feature have been automatically enabled for public repositories, but they are opt-in for private repositories.
The availability of a dependency graph allows notifying the owners of the projects when it detects a known security vulnerability in one of the dependencies and suggests known fixes from the GitHub community.
“Vulnerabilities that have CVE IDs (publicly disclosed vulnerabilities from the National Vulnerability Database) will be included in security alerts. However, not all vulnerabilities have CVE IDs—even many publicly disclosed vulnerabilities don’t have them.” states GitHub.
Github Users can choose to receive the alerts via the user interface or via email.
An initial scan conducted by GitHub revealed more than 4 million vulnerabilities in more than 500,000 repositories. Github notified affected users by December 1, more than 450,000 of the vulnerabilities were addressed either by updating the affected library or removing it altogether.
According to GitHub, vulnerabilities are in a vast majority of cases addressed within a week by active developers.
“By December 1 and shortly after we launched, over 450,000 identified vulnerabilities were resolved by repository owners either removing the dependency or changing to a secure version.” GitHub said. “Additionally, 15 percent of alerts are dismissed within seven days—that means nearly half of all alerts are responded to within a week. Of the remaining alerts that are unaddressed or unresolved, the majority belong to repositories that have not had a contribution in the last 90 days.”
A “highly critical” flaw affects Drupal 7 and 8 core, Drupal security updates expected on March 28th
23.3.2018 securityweek Vulnerebility
Drupal Security Team confirmed that a “highly critical” vulnerability affects Drupal 7 and 8 core and announced the availability of security updates on March 28th.
A “highly critical” vulnerability affects Drupal 7 and 8 core and Drupal developers are currently working to address it.
Drupal maintainers initially planned to issue a security release of Drupal 7.x, 8.3.x, 8.4.x, and 8.5.x on March 28th 2018 between 18:00 – 19:30 UTC.
The security team asked to reserve time for core updates fearing that threat actors could exploit the “highly critical security vulnerability.”
“There will be a security release of Drupal 7.x, 8.3.x, 8.4.x, and 8.5.x on March 28th 2018 between 18:00 – 19:30 UTC, one week from the publication of this document, that will fix a highly critical security vulnerability.” reads the advisory sent to the developers.
“The Drupal Security Team urges you to reserve time for core updates at that time because exploits might be developed within hours or days. “
Both Drupal 8.3.x and 8.4.x are not supported, but due to the severity of the flaw the Drupal Security Team decided to address it with specific security updates.
The Drupal CMS currently runs on over one million websites, it is the second most popular content management system behind WordPress.
“While Drupal 8.3.x and 8.4.x are no longer supported and we don’t normally provide security releases for unsupported minor releases, given the potential severity of this issue, we areproviding 8.3.x and 8.4.x releases that include the fix for sites which have not yet had a chance to update to 8.5.0.” continues the advisory.
The Drupal security team strongly recommends the following:
Sites on 8.3.x should immediately update to the 8.3.x release that will be provided in the advisory, and then plan to update to the latest 8.5.x security release in the next month.
Sites on 8.4.x should immediately update to the 8.4.x release that will be provided in the advisory, and then plan to update to the latest 8.5.x security release in the next month.
Sites on 7.x or 8.5.x can immediately update when the advisory is released using the normal procedure.