CVE-2025-39931 crypto: af_alg - Set merge to zero early in af_alg_sendmsg
A local attacker can cause a kernel crash by triggering an error in af_alg_sendmsg, leading to a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39931?
CVE-2025-39931 is a high-severity vulnerability in Linux kernel, published on 4 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-908
Which versions are affected by CVE-2025-39931?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39931?
Apply the vendor's patch.
Is CVE-2025-39931 being exploited?
There is no known exploitation of CVE-2025-39931 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-68175, AZL-75324, BELL-CVE-2025-39931, DEBIAN-CVE-2025-39931, GHSA-rfcq-q5wv-mpcg, ROOT-OS-DEBIAN-11-CVE-2025-39931 and 5 more.