What’s Vulnerable › Vulnerabilities

CVE-2025-39931: crypto: af_alg - Set merge to zero early in af_alg_sendmsg

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-10-04 · updated 2026-10-19
• Weakness: CWE-908

Description

In the Linux kernel, the following vulnerability has been resolved: crypto: af_alg - Set merge to zero early in af_alg_sendmsg If an error causes af_alg_sendmsg to abort, ctx->merge may contain a garbage value from the previous loop. This may then trigger a crash on the next entry into af_alg_sendmsg when it attempts to do a merge that can't be done. Fix this by setting ctx->merge to zero near the start of the loop.

Affected products

• Linux kernel: from 2.6.38 before 6.1.154; from 6.2 before 6.6.108; from 6.7 before 6.12.49; from 6.13 before 6.16.9; 6.17-rc1, 6.17-rc2, 6.17-rc3, 6.17-rc4, 6.17-rc5, 6.17-rc6 — fixed in 6.1.154, 6.12.49, 6.16.9, 6.6.108

How to fix

Upgrade to a fixed version: Linux kernel 6.1.154, 6.12.49, 6.16.9, 6.6.108. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/045ee26aa3920a47ec46d7fcb302420bf01fd753
• https://git.kernel.org/stable/c/2374c11189ef704a3e4863646369f1b8e6a27d71
• https://git.kernel.org/stable/c/24c1106504c625fabd3b7229611af617b4c27ac7
• https://git.kernel.org/stable/c/28f6f37abca7c5c9eb3959c66310f1d4d98b8aaf
• https://git.kernel.org/stable/c/6241b9e2809b12da9130894cf5beddf088dc1b8a
• https://git.kernel.org/stable/c/9574b2330dbd2b5459b74d3b5e9619d39299fc6f
• https://git.kernel.org/stable/c/db2b42425dfbde4983b0c20fb7cfa05f70e6a745
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-082556.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html

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