CVE-2026-31525 bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN
Undefined behavior in BPF interpreter division allows verifier mismatch, enabling out-of-bounds map access and potential 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-2026-31525?
CVE-2026-31525 is a high-severity vulnerability in Linux kernel, published on 22 Apr 2026. 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 undefined behavior in interpreter sdiv/smod for INT_MIN
The BPF interpreter's signed 32-bit division and modulo handlers use the kernel abs() macro on s32 operands. The abs() macro documentation (include/linux/math.h) explicitly states the result is undefined when the input is the type minimum. When DST contains S32_MIN (0x80000000), abs((s32)DST) triggers undefined behavior and returns S32_MIN unchanged on arm64/x86. This value is then sign-extended to u64 as 0xFFFFFFFF80000000, causing do_div() to compute the wrong result.
The verifier's abstract interpretation (scalar32_min_max_sdiv) computes the mathematically correct result for range tracking, creating a verifier/interpreter mismatch that can be exploited for out-of-bounds map value access.
Introduce abs_s32() which handles S32_MIN correctly by casting to u32 before negating, avoiding signed overflow entirely. Replace all 8 abs((s32)...) call sites in the interpreter's sdiv32/smod32 handlers.
s32 is the only affected case -- the s64 division/modulo handlers do not use abs().
Which versions are affected by CVE-2026-31525?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31525?
Apply the vendor's patch.
Is CVE-2026-31525 being exploited?
There is no known exploitation of CVE-2026-31525 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83360, BELL-CVE-2026-31525, DEBIAN-CVE-2026-31525, GHSA-jvq3-fgq9-mfpj, ROOT-OS-DEBIAN-13-CVE-2026-31525, ROOT-OS-UBUNTU-2404-CVE-2026-31525 and 1 more.