Keep your patch management pipelines primed in case another round of Citrix NetScaler patches get released soon.

The post This is Fine: What NetScaler Zero-Days Tell Us About the New Normal appeared first on SecurityWeek.

Suspected Chinese hackers with a proven knack for exploiting zero-days in security products are at it again, targeting BeyondTrust customers in attacks that researchers have traced back to late August. 

Mandiant researchers said a likely Chinese government-backed espionage group it previously tracked as UNC5221, and now calls Armory Castle, exploited the critical defect — CVE-2026-102764 — then showcased multiple tactics to escalate privileges, hop around the compromised network and evade detection. 

The same threat group has repeatedly exploited a series of defects in Ivanti products since 2023, a Citrix NetScaler zero-day widely known as CitrixBleed, and last year’s Brickstorm campaign that had an average dwell time of 400 days — all resulting in sweeping attack sprees.

“We are aware of only a small number of impacted organizations at this time, but given the stealth of the activity, and the use of a zero-day, it is possible that additional organizations were also compromised prior to the disclosure,” Kelli Vanderlee, senior analyst at Google Threat Intelligence Group, said in an email.

Mandiant warned organizations to “prepare for potential widespread exploitation,” adding that Armory Castle and other threat groups previously conducted broad, opportunistic exploitation following public vulnerability disclosures.

Mandiant and GTIG released their analysis of Armory Castle and its latest campaign as BeyondTrust publicly disclosed the vulnerability in its Remote Support product Thursday. The company’s security said it released a patch for the exploited defect for self-hosted customers Oct. 8 and automatically applied the update to cloud-based versions of the product that same day.

BeyondTrust, which conducted its own investigation and coordinated with Mandiant on an investigation involving a self-hosted customer that was compromised, noted Armory Castle’s prowess.

“This threat actor rotates its infrastructure and tooling for every victim, so attribution here rests on behavior. The indicators from one intrusion rarely survive to the next,” the company’s security team wrote in a blog post. “The threat actor has historically demonstrated a high degree of operational security awareness, professional practices, and tradecraft.”

A BeyondTrust spokesperson declined to answer questions about how many customers are already compromised or why it didn’t publicly disclose the actively exploited zero-day sooner, and instead referred back to its security advisory. 

The company said the first known instance of zero-day exploitation occurred Aug. 29, which it detected and contained Sept. 28. 

BeyondTrust also said it detected the malicious activity after zero-days were confirmed to be exploited in another security vendor’s product Sept. 27. That timing matches a round of zero-days Citrix NetScaler disclosed, following nearly two days of rampant worry and unconfirmed rumors. 

BeyondTrust did not say if there is any link or overlap between the attacks targeting Citrix NetScaler, which went undetected for more than three weeks, and its remote access product. 

GTIG researchers said there isn’t enough evidence to assess an overall targeting trend, but encouraged all potentially vulnerable organizations to apply the patch and hunt for pre-disclosure activity. 

The threat group’s previous targets include business-process outsourcers, government, legal services, technology companies and software-as-a-service providers.

“Armory Castle remains one of the most prominent China-nexus threat actors due to its persistent targeting of various edge device technologies, use of zero-day vulnerabilities for widespread exploitation across multiple industries and regions, and its continuously expanding and evolving arsenal of tools,” said Dan Perez, technical lead at GTIG.

“This is a well-established pattern for Armory Castle,” Vanderlee said. “Targeting edge devices, which typically do not support endpoint detection and response (EDR), allows the threat actor to minimize opportunities for detection and maintain stealthy, persistent access to targeted networks.”

The post Prolific Chinese espionage group exploits BeyondTrust zero-day appeared first on CyberScoop.

Critical-severity flaws could lead to authentication bypass, code execution, and sensitive authentication information leaks.

The post Citrix, Fortinet, Ivanti Patch 29 Vulnerabilities Across Their Products appeared first on SecurityWeek.

The security defect, tracked as CVE-2026-107406, could lead to remote code execution or denial-of-service.

The post Citrix Urges Immediate Patching of Critical NetScaler Vulnerability appeared first on SecurityWeek.

Citrix customers just got through back-to-back weekends filled with varying levels of uncertainty and worry, as yet another actively exploited zero-day vulnerability was discovered in Citrix NetScaler products.

Researchers and security experts said the vulnerability — CVE-2026-88779 — is less concerning because exploitation triggers denial of service and only impacts instances that have SAML (security assertion markup language) enabled. 

“This means it doesn’t work out of the box against every NetScaler deployment,” Jake Knott, head of threat intelligence at watchTowr, told CyberScoop. “While this is very inconvenient, it doesn’t have organizations scrambling to trigger incident response.”

Citrix was much quicker and consistent in alerting customers to the emerging threat Friday, and followed up the next day with a more detailed blog post and security advisory that contained a patch for the high-severity defect. 

“After we were alerted to this issue we immediately developed and published a mitigation while concurrently developing, testing and deploying a fix,” a company spokesperson said in a statement. “The fix for this issue is available, and we urge all customers to quickly apply it to their NetScaler instance.”

The Cybersecurity and Infrastructure Security Agency added the defect to its known exploited vulnerabilities catalog Sunday.

The vendor’s response also provided some relief for customers and researchers who spent much of the previous weekend rushing to assess widespread rumors of other defects in the assailed network edge gateways. In that case, Citrix took most of the weekend to confirm attackers were actively exploiting a pair of NetScaler zero-days, some of which researchers said remained undetected for at least three weeks.

“Citrix did a better job with their response to this vulnerability,” and took steps that enabled customers to make their own risk-based decisions with more currently available information, said Joe Toomey, vice president of underwriting security at insurance provider Coalition. 

“Although it’s difficult to celebrate given this is the third publicly-exploited NetScaler zero-day vulnerability in a two-week window, it is a step in the right direction,” he added. 

Citrix declined to say how many customers are impacted by the latest zero-day or when the first instance of exploitation occurred. Yet, Knott at watchTowr said exploitation likely began Friday. 

The newer defect doesn’t share any technical links with the pair of zero-days Citrix disclosed less than a week prior, but it can accelerate one of those vulnerabilities — CVE-2026-88771 — by intentionally crashing machines to speed up exploitation, Knott said.

While risk is currently perceived low for CVE-2026-88779, it is “incredibly simple to trigger, with a single specially crafted request being all that is needed to knock an appliance offline,” Knott added. “Exploitation is already occurring in the wild, and disrupting an authentication gateway can prevent legitimate users from accessing the services behind it.”

Toomey also described the denial-of-service vulnerability as less serious than the previous week’s actively exploited zero-days. Yet, he noted, exploitation attempts of CVE-2026-88779 “clearly contain shellcode that implies that the threat actor believes they can use this vulnerability, or chain it with another vulnerability, in order to achieve remote-code execution.”

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Citrix has confirmed that a new zero-day vulnerability, CVE-2026-88779, emerged just days after two other exploited flaws were patched.

The post Exploitation of Citrix NetScaler Zero-Day Hits Appliances Patched Days Earlier appeared first on SecurityWeek.

Datawater reports: Two critical NetScaler zero-days, CVE-2026-88771 and CVE-2026-88772, were used against organizations worldwide before a patch existed. CISA’s deadline is today. Patching alone will not tell you whether you were already breached. Threat level: Critical What: Two unauthenticated remote-code-execution flaws in Citrix NetScaler ADC and NetScaler Gateway, both CVSS 9.5. Status: Exploited as zero-days....

Source

Attackers remained undetected for more than three weeks as they exploited a critical zero-day vulnerability affecting Citrix NetScaler appliances en masse. 

The earliest known instance of CVE-2026-88772 exploitation occurred Sept. 3, Mandiant researchers told CyberScoop Tuesday. 

The besieged security vendor and researchers didn’t confirm the attacks until late last week. By then, Mandiant says, organizations in North America and Europe spanning the government, financial services, education, telecom, legal and professional services sectors were already likely compromised.

“We are aware of dozens of impacted organizations,” Charles Carmakal, chief technology officer at Mandiant Consulting, wrote in a LinkedIn post. He attributed the attacks to “advanced and suspected state-sponsored threat actors.”

The three-week gap — at minimum — between initial exploitation and confirmed in-the-wild attacks gave attackers a significant advantage. 

Mandiant warned that the gap could be even wider. “We are still responding to active intrusions, and new evidence may change our understanding of the campaign timeline,” researchers who published a threat intelligence report on the attacks Tuesday told CyberScoop in an email. 

The incident response firm’s analysis on the latest zero-day attack spree targeting Citrix customers underscores the multi-layered mess network defenders have been responding to since Saturday.

The zero-day exploits in Mandiant’s report only cover half of the problem. Attackers have also exploited a second Citrix NetScaler zero-day — CVE-2026-88771 — since at least Sept. 24, according to GreyNoise, but researchers said that campaign likely started earlier as well.

It’s unclear to what extent the pair of zero-days are linked. But, nearly two days after the first unconfirmed rumors of the attacks surfaced, Citrix disclosed both of the actively exploited defects in a security advisory Sunday, releasing patches for them and six additional vulnerabilities.

Mandiant researchers uncovered multiple novel tools and tactics attackers used to exploit CVE-2026-88772, gain privileged access to compromised environments, hop around the network and steal sensitive data. A threat actor in one observed intrusion routed traffic through novel tunneler malware to “manually conduct internal reconnaissance and credential theft,” researchers wrote. 

Researchers at watchTowr also published technical analysis of CVE-2026-88782 Tuesday.

The attacks from multiple fronts, involving two zero-days, reflect an alarming and sustained pattern of malicious activity targeting so-called edge devices, such as virtual private network gateways and firewalls. 

Vulnerabilities in these devices accounted for 48% of the enterprise-related zero-days last year, according to Google Threat Intelligence Group.

“Our previous research corroborates that both cyber espionage and financially motivated threat actors prioritize exploiting vulnerabilities in edge devices and security appliances,” Mandiant researchers wrote in response to questions on their report. 

“Because most edge devices do not support endpoint detection and response (EDR) monitoring, targeting them, particularly through exploiting zero-day vulnerabilities, provides threat actors with an infection vector that is difficult to detect and prevent, and the opportunity to scale a campaign as long as the exploit remains undiscovered,” the researchers added. 

Carmakal, in his LinkedIn post, warned that Mandiant expects “broad and opportunistic exploitation” of both of the Citrix NetScaler zero-days by a variety of threat actors in the near term.

The post Attackers exploited Citrix NetScaler zero-day for at least three weeks undetected appeared first on CyberScoop.

Citrix took most of the weekend to confirm that attackers were actively exploiting the newest round of NetScaler zero-days, leaving network defenders and threat hunters to react without official confirmation. 

Yet, behind the scenes, multiple CERTs, advisory firms, insurance providers, researchers and chatty security professionals warned their respective peers and communities of a live and serious threat. 

Nearly two days after the first unconfirmed rumors, Citrix published a security advisory Sunday disclosing the exploited zero-days, CVE-2026-88771 and CVE-2026-88772, releasing patches for them and six additional defects.

By then, criticism was at a fever pitch, and for some NetScaler customers the warning came too late. 

“The information vacuum was most striking. Customers were receiving warnings through unofficial channels while Citrix remained publicly silent,” Ben Harris, founder and CEO at watchTowr, told CyberScoop. 

“Customers were left without communication, guidance, or even acknowledgement that the vulnerability that was rumored to exist was real. Citrix could have warned customers that active exploitation was occurring and provided immediate defensive guidance without disclosing technical details that would help attackers,” he added. 

“When active exploitation is underway, hours matter,” Harris said.

Citrix did not directly answer questions about the lengthy communication delay. 

“We recently identified critical vulnerabilities in Citrix NetScaler ADC and Citrix NetScaler Gateway that led us to immediately develop and release a new version of the software that addresses the issues,” the company said in a prepared statement.

The critical defects are both rated 9.5 on the CVSS scale and allow attackers to achieve remote code execution. 

Researchers are particularly concerned about CVE-2026-88771, a command-injection vulnerability that affects all NetScaler appliances in a default configuration. That gives attackers a broad pool of targets and a better chance at successful exploitation. A proof-of-concept exploit for the vulnerability is also publicly available. 

Palo Alto Networks said it identified more than 50,000 publicly exposed instances of Citrix NetScaler devices potentially vulnerable to both of the zero-days as of Sunday. 

The earliest known exploitation attempt occurred Sept. 24 when GreyNoise said it observed an unsuccessful exploitation attempt against a Citrix NetScaler Gateway under its control for malicious activity scanning purposes. But researchers warn that exploitation likely started before then.

Citrix did not say how many customers have been compromised thus far and researchers are still assessing the fallout.

Citrix said it is making generic indicators of compromise available to customers in their user consoles, and the company referred to previously issued guidance for customers who suspect compromise. 

Attribution for the attacks is also still under investigation, yet NetScaler products are a common, recurring target for financially-motivated cybercriminals and state-sponsored espionage groups. 

The Cybersecurity and Infrastructure Security Agency issued an alert Sunday after Citrix publicly confirmed the attacks on its customers, and added CVE-2026-88771 and CVE-2026-88772 to its known exploited vulnerabilities catalog. The vendor has appeared on the agency’s list of vulnerabilities known to be exploited five times this year, and a total of 26 times since late 2021.

Security leaders across the industry — including Charles Carmakal, chief technology officer at Mandiant Consulting, and Wendi Whitmore, chief security intelligence officer at Palo Alto Networks — also sprung into action Sunday, with direct warnings on LinkedIn about the urgent threat. 

The information vacuum that persisted through most of the weekend put cybersecurity professionals in sometimes unique positions. Joe Toomey, vice president of underwriting security at insurance provider Coalition, said the company notified potentially vulnerable customers with limited official data and no confirmation from CISA or Citrix.

In a LinkedIn post Sunday, he called Citrix “unconscionably irresponsible” for remaining silent for more than 36 hours after word began circulating about in-the-wild exploitation.

“I fully understand a vendor embargoing specific details about a vulnerability when a patch has not yet been published, but once the vuln is exploited in the wild, some of those rules no longer apply,” Toomey wrote.

Citrix and its customers are in familiar territory. The vendor’s products have been widely targeted in previous attack sprees, often involving zero-day exploits and some infamously referred to as CitrixBleed and CitrixBleed 2.

“Citrix has a history of delaying the publication of vulnerabilities, even when they’re being exploited in the wild and affecting customers. Citrix eventually released patches and an advisory, but an adequate response also requires timely, clear communication,” Harris said. 

“Customers shouldn’t have to rely on unofficial warnings, security researchers, and third parties to learn that critical infrastructure may already be compromised,” he added. “This latest incident raises serious questions about whether Citrix has learned from previous crises and meaningfully improved how it protects and informs customers.”

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Citrix published a security bulletin Tuesday disclosing six vulnerabilities in NetScaler ADC and NetScaler Gateway appliances, including a high-severity memory disclosure flaw that researchers say belongs to a vulnerability class first identified in the 2023 incident known as CitrixBleed.

The company rated the overall bulletin severity as high and assigned CVSS scores ranging from 6.9 to 8.8 across the six CVEs. Citrix said customers should install the updated builds and, in one case, manually adjust a configuration parameter even after patching.

The most closely scrutinized of the vulnerabilities, CVE-2026-8451, was discovered by researchers at watchTowr, a cybersecurity firm that has published several prior analyses of issues in NetScaler products. According to a technical writeup the firm released alongside Tuesday’s disclosure, the vulnerability stems from how NetScaler parses SAML authentication requests when an appliance is configured as a SAML identity provider, a deployment mode commonly used for single sign-on.

WatchTowr researcher Aliz Hammond wrote that the firm found the flaw in late March while reproducing a separate vulnerability, CVE-2026-3055, that Citrix disclosed earlier this year. That March flaw was added to CISA’s Known Exploited Vulnerabilities catalog after researchers and the agency confirmed active exploitation within days of disclosure. The new flaw shares a root cause with the March bug: both involve out-of-bounds memory reads triggered by malformed SAML requests sent to NetScaler’s authentication endpoints.

“Referencing what we wrote previously, because it is demonstrably evergreen: ‘However, what should be of concern is the bigger picture – the trend, which is very clearly suggesting that memory management continues to appear fragile within Citrix NetScaler appliances, to the extent that even accidentally misconfiguring an appliance can lead to the disclosure of leaked memory,’” Hammond wrote in the report. 

The bulletin also discloses five additional vulnerabilities affecting different NetScaler subsystems. Two involve memory overflow conditions that could cause denial-of-service outcomes. A separate flaw could allow unauthenticated arbitrary file reads on appliances where management access is exposed on certain network interfaces. Another concerns memory overread triggered through TCP timestamp handling. The sixth involves a denial-of-service condition tied to malformed HTTP/2 requests, which requires an additional manual configuration change to fully fix, since the relevant timeout parameter defaults to a value that leaves the underlying condition unaddressed unless administrators set it explicitly.

Along with Hammond, the bulletin credits Michael Tucker of the XOR team at JPMorgan Chase and Maxim Suhanov for finding the vulnerabilities. 

The NetScaler product line has accumulated more than 20 entries in CISA’s KEV catalog over the past three years, including multiple flaws that have been weaponized in ransomware campaigns. As of Tuesday, the latest vulnerability had not joined that list — neither the vendor bulletin nor watchTowr’s writeup cited confirmed exploitation at the time of disclosure.

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