CVE-2025-40204: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-40204 is a vulnerability discovered in the Linux kernel's SCTP (Stream Control Transmission Protocol) implementation, specifically related to MAC comparison timing. The vulnerability was disclosed on November 12, 2025, and affects various Linux distributions and their kernel packages (NVD, Red Hat).

The vulnerability stems from a non-constant-time MAC comparison in the SCTP implementation. The issue involves the way Message Authentication Codes (MACs) are compared, which could potentially expose timing information. The vulnerability has been assigned a CVSS v3.1 base score of 5.3 (medium severity) with an attack vector requiring adjacent network access and high attack complexity (Snyk).

The vulnerability could lead to information exposure through timing attacks. According to the CVSS metrics, a successful exploitation could result in a total loss of confidentiality, though there is no direct impact on system integrity or availability (Snyk).

The vulnerability has been fixed by implementing constant-time MAC comparison using appropriate helper functions. Various Linux distributions have released or are in the process of releasing patches. For instance, Debian has fixed the issue in version 6.1.158-1 for bookworm and 6.17.8-1 for sid (Debian).