Listen to this Post
A Dangerous Déjà Vu for Citrix NetScaler Devices
A new vulnerability dubbed CitrixBleed2 (CVE-2025-5777) has surfaced, and
The vulnerability allows attackers to extract memory contents and steal session tokens using nothing more than malformed login requests. Researchers warn that while Citrix insists there is “no current evidence” of active exploitation, multiple cybersecurity firms and analysts have already seen signs that threat actors are leveraging this weakness in the wild. The situation is further complicated by Citrix’s delayed acknowledgment and lack of transparency around indicators of compromise (IOCs), putting businesses at risk even as patches have been released.
Vulnerability Overview: CitrixBleed2 Under the Microscope
A Familiar Flaw Returns
CitrixBleed2, tagged as CVE-2025-5777, is a critical security flaw in Citrix NetScaler appliances. It shares a striking resemblance to 2023’s CitrixBleed bug, using similarly simple exploitation techniques that can have devastating consequences. By crafting a malformed POST request — specifically by omitting the equal sign in the login parameter — attackers can trick the system into leaking uninitialized memory.
Technical Breakdown
The bug resides in how Citrix appliances handle string formatting in C. Using the snprintf function with the %.s format specifier, the application prints data from memory until it encounters a null byte. This means each request can leak around 127 bytes of data. And since attackers can automate repeated requests, sensitive information like session tokens can be harvested rapidly.
Exploitation Confirmed
While watchTowr researchers initially failed to retrieve sensitive information through their test runs, Horizon3 successfully exploited the vulnerability and even published video proof demonstrating the extraction of session tokens. They warned that this flaw also impacts admin-side configuration tools — expanding the attack surface significantly.
Disputed Claims About Exploitation
Despite Citrix’s claims that no exploitation has been observed, other experts disagree. Kevin Beaumont, a well-known security researcher, argues that exploitation began in mid-June, identifying patterns in NetScaler logs consistent with memory harvesting attacks. His indicators of compromise include repeated POST requests with specific byte signatures, log anomalies, and manipulated usernames.
Patches and Mitigation
Citrix has released patches for CVE-2025-5777 and urges organizations to install them without delay. However, merely applying patches may not be enough. Admins are also advised to inspect user session logs, look for anomalies, and terminate all active sessions to eliminate potential hijacks. The release of public PoCs means this flaw is likely to become a mainstream attack vector very quickly.
What Undercode Say:
The Pattern of Disclosure and Denial
CitrixBleed2 reveals a recurring problem within the vendor community — delayed response and undercommunication. The original CitrixBleed incident was similarly downplayed before becoming one of the year’s most widely exploited bugs. Once again, Citrix’s stance of “no evidence of exploitation” is being openly challenged by researchers with access to threat intelligence and real-world telemetry.
Impact on Enterprise Security
The most concerning element of CVE-2025-5777 is its simplicity. No buffer overflows, no complex shellcode — just a malformed login string. For organizations relying on Citrix for remote access or application delivery, this vulnerability undermines core infrastructure trust. Attackers don’t need elevated privileges or lateral movement strategies when a gateway allows direct memory extraction.
Detection and Logging Gaps
Beaumont’s analysis highlighted another critical issue: lack of logging clarity in Citrix appliances. The inability to catch and correlate malformed POST attempts means exploitation can go undetected for extended periods. Without IOCs from the vendor itself, organizations must rely on the wider security community, which shouldn’t be the case for a product so central to enterprise networking.
The Role of Public Exploits
The release of PoC exploits shifts CVE-2025-5777 into high-risk territory. While patches are available, many organizations delay updates for operational reasons. Meanwhile, automated scanning tools and script kiddies can now reproduce Horizon3’s attack with minimal effort. Citrix’s call to action should have been louder and clearer — especially given their history with similar flaws.
Risks to Cloud and Admin Interfaces
Beyond user session hijacking,
Recommendations Moving Forward
1. Immediate patching is non-negotiable.
2. Review all ICA and PCoIP sessions for anomalies.
3. Implement network-layer protections to detect malformed login POSTs.
4. Monitor public scanning attempts on known NetScaler ports.
- Consider segmentation and isolation of Citrix infrastructure to limit blast radius in case of breach.
Reputational Concerns for Citrix
Citrix’s ongoing pattern of downplaying vulnerabilities may begin to hurt its standing in the enterprise security market. While developing secure code is always a challenge, refusing to acknowledge real-world exploits only delays customer response and magnifies the damage when attacks do occur. Transparency, not silence, builds trust.
🔍 Fact Checker Results:
✅ Exploitation of CitrixBleed2 is technically confirmed through
❌ Citrix’s claim of no active exploitation is disputed by multiple independent experts
✅ PoC exploits are publicly available, increasing the urgency of patch deployment
📊 Prediction:
Expect widespread scanning and exploitation of CVE-2025-5777 in the coming weeks, especially against unpatched Citrix NetScaler devices. Threat actors will likely incorporate this into ransomware campaigns, targeting VPN and remote access infrastructures. If Citrix fails to provide clearer threat intelligence and indicators of compromise, more organizations will fall victim to silent breaches before realizing the severity of the flaw.
References:
Reported By: www.bleepingcomputer.com
Extra Source Hub:
https://www.quora.com/topic/Technology
Wikipedia
OpenAi & Undercode AI
Image Source:
Unsplash
Undercode AI DI v2
