CVE-2025-40109: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-40109 was published on November 9, 2025, affecting the Linux kernel. The vulnerability relates to ensuring that set_ent is always present in the crypto random number generator (RNG) subsystem, since only the deterministic random bit generator (DRBG) provides it (NVD).

The vulnerability exists in the Linux kernel's cryptographic random number generator (RNG) subsystem. The issue specifically involves the set_ent functionality, which was not consistently present across all implementations, with only the DRBG (Deterministic Random Bit Generator) providing this feature (NVD).

This vulnerability is part of a larger set of security issues that could potentially lead to privilege escalation, denial of service, or information leaks in the Linux kernel (Debian Security).

The vulnerability has been fixed in various Linux distributions. For Debian's oldstable distribution (bookworm), the fix was implemented in version 6.1.158-1 (Debian Security). Ubuntu has also released patches for affected versions, with fixes available for various kernel variants including linux-azure, linux-gcp, and linux-aws (Ubuntu Security).