CVE-2025-34451 is a stack-based buffer overflow vulnerability identified in the open-source tool proxychains-ng, specifically in versions up to 4.17 and prior to commit cc005b7. The vulnerability resides in the proxy_from_string() function within src/libproxychains.c, which processes proxy configuration strings. When an attacker supplies crafted proxy configuration entries containing excessively long username or password fields, the function writes beyond the bounds of fixed-size stack buffers. This buffer overflow can corrupt adjacent memory on the stack, potentially causing application crashes (denial of service) or, in certain execution environments, enabling further exploitation such as arbitrary code execution. The vulnerability does not require authentication or user interaction but does require local access to the system to supply malicious proxy configuration data. The CVSS 4.0 vector indicates local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and high impact on availability (VA:H) with no impact on confidentiality or integrity. No public exploits have been reported yet, but the presence of a stack-based buffer overflow in a widely used proxy chaining tool suggests a significant risk if exploited. Proxychains-ng is commonly used by security professionals and penetration testers to route network traffic through proxies, so environments relying on this tool for anonymization or network routing could be disrupted or compromised. The vulnerability was published on December 18, 2025, and no patch links are currently provided, indicating users must monitor for updates or apply manual mitigations.

For European organizations, the primary impact of CVE-2025-34451 is the potential for denial of service in systems utilizing proxychains-ng for network traffic routing or anonymization. This could disrupt security operations, penetration testing activities, or any automated processes relying on proxychains-ng, leading to operational downtime. In environments where proxychains-ng is integrated into security tooling or network infrastructure, memory corruption could be leveraged for privilege escalation or arbitrary code execution, posing a risk to system integrity and confidentiality. Given the local attack vector, the threat is more pronounced in environments with multiple users or where untrusted users have local access. Organizations in sectors with stringent data protection requirements, such as finance, healthcare, and critical infrastructure, could face compliance and reputational risks if this vulnerability leads to exploitation. Additionally, disruption of security tools could impair incident response capabilities. The absence of known exploits reduces immediate risk but does not eliminate the potential for future attacks, especially as the vulnerability becomes more widely known.

European organizations should immediately audit their use of proxychains-ng and identify affected versions (up to 4.17 and prior to commit cc005b7). Until an official patch is released, users should avoid processing untrusted proxy configuration files containing user-supplied username or password fields. Implement strict input validation and length checks on proxy configuration entries to prevent buffer overflow conditions. Restrict local access to systems running proxychains-ng to trusted users only and monitor for unusual crashes or behavior indicative of exploitation attempts. Employ application whitelisting and memory protection mechanisms such as stack canaries, ASLR, and DEP to reduce exploitation likelihood. Regularly check the official rofl0r proxychains-ng repository or trusted vulnerability databases for patches or updates addressing this issue. For critical environments, consider alternative proxy chaining tools with no known vulnerabilities until this issue is resolved. Finally, integrate this vulnerability into vulnerability management and incident response workflows to ensure timely detection and remediation.