CVE-2025-40182: 
Linux Debian vulnerability analysis and mitigation

CVE-2025-40182 is a memory corruption vulnerability in the Linux kernel's symmetric key cipher (skcipher) framework, caused by improper request size (reqsize) initialization. The flaw was introduced when commit afddce13ce81d added the cra_reqsize field to the crypto_alg struct, which was intended for ahash and acomp algorithm types but was incorrectly recommended for use in all crypto algorithms including skcipher. When cra_reqsize is used in skcipher algorithms without the corresponding framework-level initialization, memory corruptions and kernel crashes result. The vulnerability was published on November 12, 2025, and affects Linux kernel versions from commit afddce13ce81d52a13898fa0700917835c71acd6 up to the fix commits. No CVSS score has been assigned by NVD at this time; the EPSS score is 0.00018 (very low) (Feedly, NVD).

The root cause is improper initialization of the reqsize field in the Linux kernel's skcipher algorithm framework (CWE not formally assigned by NVD). When a skcipher algorithm driver sets cra_reqsize in the crypto_alg struct instead of calling crypto_skcipher_set_reqsize(), the skcipher framework's init function does not propagate this value correctly, leaving the request context buffer undersized or uninitialized. Subsequent cryptographic operations that rely on the request context then access out-of-bounds memory, leading to memory corruption and potential kernel crashes. The fix adds proper set_reqsize calls in the skcipher init function to correctly initialize reqsize from cra_reqsize for affected algorithms. A crash reproduction case is publicly documented by the reporter (Feedly, NVD, Crash PoC).

Successful triggering of this vulnerability results in kernel memory corruption and system crashes (denial of service). Because the corruption occurs in kernel memory during cryptographic request processing, it could potentially be leveraged for privilege escalation or information disclosure depending on the specific memory layout, though no such exploitation has been demonstrated publicly. The impact is primarily an availability concern — affected systems using skcipher algorithms with cra_reqsize set may experience unexpected kernel panics or instability (Feedly, NVD).

There is no evidence of active in-the-wild exploitation of CVE-2025-40182. A crash reproduction proof-of-concept is publicly available via a GitHub Gist linked in the kernel commit message, demonstrating the memory corruption and crash behavior. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is 0.00018, indicating a very low probability of exploitation in the near term. Detection plugins are available from Nessus (plugin 275344) and Qualys (IDs 6031981, 6032019) (Feedly, Tenable, Crash PoC).

The fix is included in Linux kernel stable commits f041339d6b9a5a46437f0c48fc7279c92af7a513 and 229c586b5e86979badb7cb0d38717b88a9e95ddd, and is present in kernel version 6.17.4 and the 6.18-rc1 release. Administrators should update to a patched kernel version as soon as it is available for their distribution. As a workaround, avoid using cra_reqsize in skcipher algorithm drivers and use crypto_skcipher_set_reqsize() instead, as recommended by the upstream fix (Feedly, Kernel Patch 1, Kernel Patch 2).