CVE-2025-39917 bpf: Fix out-of-bounds dynptr write in bpf_crypto_crypt
A local attacker with root privileges can trigger an out-of-bounds write in the Linux kernel's BPF crypto subsystem, potentially leading to code execution or privilege escalation.
- 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-2025-39917?
CVE-2025-39917 is a high-severity memory corruption vulnerability in Linux kernel, published on 1 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:
bpf: Fix out-of-bounds dynptr write in bpf_crypto_crypt
Stanislav reported that in bpf_crypto_crypt() the destination dynptr's size is not validated to be at least as large as the source dynptr's size before calling into the crypto backend with 'len = src_len'. This can result in an OOB write when the destination is smaller than the source.
Concretely, in mentioned function, psrc and pdst are both linear buffers fetched from each dynptr:
psrc = __bpf_dynptr_data(src, src_len); [...] pdst = __bpf_dynptr_data_rw(dst, dst_len); [...] err = decrypt ? ctx->type->decrypt(ctx->tfm, psrc, pdst, src_len, piv) : ctx->type->encrypt(ctx->tfm, psrc, pdst, src_len, piv);
The crypto backend expects pdst to be large enough with a src_len length that can be written. Add an additional src_len > dst_len check and bail out if it's the case. Note that these kfuncs are accessible under root privileges only.
Weakness: CWE-787
Which versions are affected by CVE-2025-39917?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39917?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2025-39917 being exploited?
There is no known exploitation of CVE-2025-39917 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39917, DEBIAN-CVE-2025-39917, GHSA-8xqx-42cr-fv84, UBUNTU-CVE-2025-39917.