A critical security vulnerability designated as CVE-2025-5777 has been discovered in Citrix NetScaler ADC and NetScaler Gateway products, creating significant exposure risks for enterprise networks worldwide. Security researchers have dubbed this flaw “Citrix Bleed 2” due to its striking resemblance to the notorious 2023 vulnerability that wreaked havoc across corporate infrastructures globally.
Understanding the CVE-2025-5777 Vulnerability
The newly identified vulnerability stems from an out-of-bounds memory read issue that specifically affects NetScaler devices configured as gateway appliances. Organizations operating virtual servers for VPN, ICA Proxy, Clientless VPN (CVPN), RDP Proxy, or AAA authentication services face the highest risk exposure from this security flaw.
What makes this vulnerability particularly dangerous is its similarity to CVE-2023-4966, the original Citrix Bleed vulnerability that was extensively exploited by ransomware operators and nation-state threat actors throughout 2023. The recurrence of such a critical flaw in widely-deployed network infrastructure highlights ongoing security challenges in enterprise gateway solutions.
Technical Exploitation Mechanism
According to comprehensive analysis conducted by watchTowr and Horizon3 security researchers, attackers can exploit this vulnerability through specially crafted POST requests during authentication attempts. The attack vector involves manipulating the login parameter by removing the equals sign or associated value, creating a malformed request that triggers the memory disclosure.
When processed by the vulnerable NetScaler device, these malicious requests cause the system to expose memory contents up to the first null byte in the InitialValue response section. The root cause lies in improper implementation of the snprintf function combined with the %.*s format string, resulting in unintended memory data leakage.
Attack Scope and Security Implications
Each successful exploitation attempt yields approximately 127 bytes of sensitive data from the device’s memory. However, threat actors can execute multiple sequential requests to extract additional information, significantly amplifying the potential damage. Horizon3 researchers have successfully demonstrated the ability to steal user session tokens, providing attackers with unauthorized access to corporate systems and sensitive data.
The cybersecurity community faces heightened concerns as proof-of-concept exploit code has already surfaced in public repositories, dramatically lowering the technical barrier for potential attackers. This accessibility increases the likelihood of widespread exploitation attempts across vulnerable NetScaler deployments.
Evidence of Active Exploitation
Despite official statements from Citrix representatives claiming no confirmed exploitation cases, independent security researchers report contradictory evidence. Cybersecurity expert Kevin Beaumont indicates that the vulnerability has been actively exploited since mid-June, while ReliaQuest previously issued warnings about suspicious activity patterns targeting NetScaler infrastructures.
Mitigation Strategies and Security Patches
Citrix has responded promptly by releasing security patches to address the CVE-2025-5777 vulnerability. The company strongly recommends that system administrators not only apply the available updates but also terminate all active ICA and PCoIP sessions following patch deployment. This additional step prevents potential access through previously compromised session tokens.
Organizations should immediately conduct comprehensive inventories of their NetScaler device deployments and prioritize security update installation. Enhanced monitoring of network traffic patterns and authentication logs can help identify potential exploitation attempts or compromise indicators.
The emergence of Citrix Bleed 2 reinforces the critical importance of proactive security patch management and continuous threat monitoring in enterprise environments. Organizations must establish robust incident response procedures and conduct regular security assessments of their network infrastructure to minimize exposure to sophisticated cyber threats. Given the proven track record of Citrix vulnerabilities being targeted by advanced persistent threat groups, immediate remediation action is essential for maintaining organizational security posture.
