CVE-2026-74371
HIGHCVE-2026-74371 is a high-severity (CVSS 7.8) vulnerability in Kernel. O3 Security confirms whether CVE-2026-74371 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
bpf: fix BPF_PROG_QUERY OOB write and cgroup backward compat
Real-World Exposure
KernelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 6.17.0&&< 6.18.40 | 6.18.40 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Kernel to 6.18.40 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-74371 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-74371 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-74371. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-74371 in your dependencies?
O3 detects CVE-2026-74371 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.