CVE-2025-52936 is a critical security vulnerability classified under CWE-59, which pertains to Improper Link Resolution Before File Access, commonly known as 'Link Following'. This vulnerability affects the yrutschle sslh software, specifically all versions before 2.2.2. The issue arises when sslh improperly resolves symbolic links before accessing files, potentially allowing an attacker with limited privileges to manipulate file access paths. This can lead to unauthorized access or modification of files that should otherwise be protected. The vulnerability has a CVSS 4.0 base score of 9.3, indicating a critical severity level. The vector details show that exploitation requires local access (AV:L), low attack complexity (AC:L), no user interaction (UI:N), and low privileges (PR:L). The impact on confidentiality (C), integrity (I), and availability (A) is high or low depending on the specific vector components, with high confidentiality and integrity impact and low availability impact. The vulnerability does not require authentication (AT:N) but does require local privileges and user interaction is not needed. The scope is unchanged (S:N), meaning the vulnerability affects the same security scope. The vulnerability is currently not known to be exploited in the wild. The root cause is the software's failure to securely handle symbolic links before file operations, which can be exploited to access or overwrite sensitive files by redirecting file paths via symbolic links. Since sslh is a tool that multiplexes incoming connections on a single port to different backend servers based on protocol detection, improper file access could potentially be leveraged to compromise the host system or escalate privileges.

For European organizations, the impact of CVE-2025-52936 can be significant, especially for those relying on sslh for managing network traffic and protocol multiplexing. Exploitation could lead to unauthorized disclosure of sensitive information, modification of critical configuration files, or disruption of services by manipulating file access paths. This could affect confidentiality and integrity of data, potentially leading to data breaches or service interruptions. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure that use sslh as part of their network stack are at higher risk. The requirement for local access means that attackers would need some foothold in the network or system, but once achieved, the vulnerability could facilitate privilege escalation or lateral movement. Given the critical severity and the potential for serious impact on system security, European organizations must prioritize remediation. The lack of known exploits in the wild provides a window for proactive mitigation before active attacks emerge.

1. Immediate upgrade to sslh version 2.2.2 or later, where the vulnerability is fixed, is the most effective mitigation. 2. If upgrading is not immediately possible, restrict local access to systems running sslh by enforcing strict access controls and monitoring for suspicious local activity. 3. Implement file system integrity monitoring to detect unauthorized changes to critical files that could be targeted via symbolic link manipulation. 4. Employ mandatory access controls (e.g., SELinux, AppArmor) to limit sslh's file system permissions, preventing it from following or accessing unauthorized symbolic links. 5. Conduct regular audits of symbolic links in directories accessed by sslh to identify and remove potentially malicious links. 6. Use network segmentation and host-based firewalls to limit exposure of systems running sslh to only trusted users and services. 7. Monitor logs for unusual file access patterns or errors related to symbolic links that could indicate exploitation attempts. 8. Educate system administrators about the risks of CWE-59 vulnerabilities and secure file handling best practices to prevent similar issues.