CVE-2026-74371 bpf: fix BPF_PROG_QUERY OOB write and cgroup backward compat
An out-of-bounds write in the Linux kernel BPF subsystem allows attackers to potentially execute code or escalate privileges via crafted BPF_PROG_QUERY calls.
- 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-2026-74371?
CVE-2026-74371 is a high-severity memory corruption vulnerability in Linux, published on 15 Aug 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 BPF_PROG_QUERY OOB write and cgroup backward compat
BPF_PROG_QUERY writes back the 'query.revision' field unconditionally to userspace. If userspace passes a smaller 'bpf_attr' structure (e.g. 40 bytes, which was the layout before the addition of 'query.revision'), the kernel performs an out-of-bounds write.
Fix this by propagating the user-provided attribute size 'uattr_size' down to the cgroup query handlers, and conditionally skipping writing the revision field to userspace when the provided buffer size is insufficient.
query.revision in bpf_mprog_query is structurally identical to the cgroup case: a late tail field, written unconditionally.
But the backward-compat hazard is not the same.
The min-historical-size test is per command, and bpf_mprog_query only serves attach types that were born with revision in the struct:
- tcx_prog_query -> BPF_TCX_INGRESS/EGRESS - netkit_prog_query -> BPF_NETKIT_PRIMARY/PEER
tcx, netkit, the revision field, and bpf_mprog_query itself all landed in the same v6.6 merge window (053c8e1f235d added the mprog query API + revision; tcx in e420bed02507, netkit in 35dfaad7188c). There has never been a tcx/netkit BPF_PROG_QUERY userspace that doesn't know about revision. So for these commands the minimum legitimate struct already covers offset 56-64 — no old binary can be broken here.
Contrast with cgroup: BPF_PROG_QUERY on cgroup attach types shipped in 2017; revision write-back was bolted on years later (120933984460). That path has a real population of pre-revision callers.
Which versions are affected by CVE-2026-74371?
How do I fix CVE-2026-74371?
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-2026-74371 being exploited?
There is no known exploitation of CVE-2026-74371 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-74371, DEBIAN-CVE-2026-74371, GHSA-wg9f-h9hg-j36p, UBUNTU-CVE-2026-74371.