A critical security flaw, designated as CVE-2025-5777 and colloquially known as CitrixBleed2, has been identified in Citrix NetScaler ADC and Gateway products. This vulnerability permits unauthorized attackers to extract up to 127 bytes of sensitive data per request, potentially compromising session tokens and user credentials through memory disclosure attacks.
Understanding the Vulnerability
The root cause of CitrixBleed2 lies in improper memory management within the NetScaler Packet Parsing Engine (nsppe binary), which is integral to NetScaler Gateway features and AAA (Authentication, Authorization, and Accounting) authentication mechanisms. Specifically, the flaw is exploited via the `/p/u/doAuthentication.do` endpoint, responsible for processing login requests. When the system parses a login form key without validating the presence of associated form values, it causes the `param_2` structure to point to adjacent memory. This oversight results in the leakage of exactly 127 bytes of arbitrary data, as the memory becomes null-terminated within the function.
Potential Impact
Exploitation of this vulnerability can lead to several severe consequences:
– Session Hijacking: Attackers can capture session tokens, enabling them to impersonate legitimate users and gain unauthorized access to systems.
– Credential Theft: The shared memory space may contain plaintext credentials from concurrent users, allowing attackers to harvest sensitive information.
– Administrative Access: Exposure of high-privilege nsroot session tokens can grant attackers complete control over NetScaler ADC instances.
Affected Versions
The vulnerability impacts multiple versions of NetScaler ADC and Gateway products released before specific patches in June 2025. Affected versions include:
– NetScaler ADC and NetScaler Gateway 14.1 prior to 14.1-43.56
– NetScaler ADC and NetScaler Gateway 13.1 prior to 13.1-58.32
– NetScaler ADC 13.1-FIPS and NDcPP prior to 13.1-37.235-FIPS and NDcPP
– NetScaler ADC 12.1-FIPS prior to 12.1-55.328-FIPS
It’s important to note that the vulnerability extends beyond regular user endpoints to configuration utilities used by administrators, thereby increasing the risk of high-privilege credential exposure.
Proof-of-Concept Exploits Released
Security researchers have developed and released proof-of-concept (PoC) exploits demonstrating the ease with which this vulnerability can be exploited. By sending malformed authentication requests with missing form values to the vulnerable endpoint, attackers can trigger the system to reflect unintended memory contents in responses. This method effectively allows the extraction of sensitive data without requiring authentication.
Mitigation and Recommendations
To protect systems from potential exploitation, it is imperative for organizations to take the following actions:
1. Apply Security Patches: Citrix has released patches addressing this vulnerability. Organizations should immediately upgrade to the following versions:
– NetScaler ADC and NetScaler Gateway 14.1-43.56 and later releases
– NetScaler ADC and NetScaler Gateway 13.1-58.32 and later releases
– NetScaler ADC 13.1-FIPS and 13.1-NDcPP 13.1-37.235 and later releases
– NetScaler ADC 12.1-FIPS 12.1-55.328 and later releases
2. Terminate Active Sessions: After applying the patches, terminate all active sessions to prevent potential misuse of stolen session tokens.
3. Monitor System Logs: Regularly review logs for unusual activities or anomalies that may indicate attempted exploitation.
4. Audit Configurations: Ensure that all configurations are reviewed and unauthorized changes are addressed promptly.
Conclusion
The CitrixBleed2 vulnerability poses a significant threat to organizations utilizing affected NetScaler products. Given the availability of PoC exploits and the potential for widespread exploitation, immediate action is required to secure systems. By applying the recommended patches and following best practices for system monitoring and configuration management, organizations can mitigate the risks associated with this critical vulnerability.
