CVE-2025-39917: bpf: Fix out-of-bounds dynptr write in bpf_crypto_crypt

Vulnerability summary

CVE-2025-39917 is a high (CVSS 7.8) Out-of-bounds Write vulnerability in linux. EPSS estimates a 0.15% chance of exploitation in the next 30 days, higher than 4.2% of scored vulnerabilities.

Timeline

1. 01-10-2025
   PublishedVulnerability first disclosed.
2. 11-05-2026
   Last modifiedVulnerability information updated.

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.

• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.