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CVE-2026-74371
bpf: fix BPF_PROG_QUERY OOB write and cgroup backward compat
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem include/linux. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74371 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
include/linux/bpf-cgroup.h
kernel/bpf/cgroup.c
kernel/bpf/syscall.c
- What this is
- BPF [CORE]MAINTAINERS section matched on include/linux/bpf* · bpf@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_BPF|CONFIG_CGROUP_BPF' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switches
- CONFIG_BPF, CONFIG_CGROUP_BPF
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 6.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- include/linux
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12.110 | 6.12.110 | b78eb6efbf05 |
| 6.17 | 6.18.40 | a7131340d0f9 |
| 6.17 | 7.1.5 | d3d630e8a7f3 |
| 6.17 | 7.2 | 21c4b99b27f3 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The flaw is reached only through the bpf(2) syscall BPF_PROG_QUERY command on cgroup attach types via __sys_bpf()→bpf_prog_query()→cgroup_bpf_prog_query(); per kernel CNA guidance BPF/tc/netlink paths are Local, not Network.
- AC:LAttack complexity, low
- The attacker fully controls the bpf_attr buffer, its declared size (e.g. 40 bytes pre-revision), placement in memory, cgroup2 target_fd, and attach_type; passing a short size reliably triggers the 8-byte revision copy_to_user at offset 56 with no race or external precondition.
- PR:LPrivileges required, low
- bpf_prog_query() enforces bpf_net_capable(), requiring CAP_NET_ADMIN or CAP_SYS_ADMIN; both are delegable and obtainable inside an unprivileged user namespace (unshare -Urn) on typical distributions, so this is Low rather than init-namespace administrator.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own bpf(BPF_PROG_QUERY) syscall (or an auto-invoked legacy-sized query after kernel upgrade); no separate victim mount, file open, or interactive action is needed.
- S:UScope, unchanged
- copy_to_user() writes past the caller-supplied userspace buffer boundary, corrupting adjacent mappings in the calling process; it does not corrupt kernel heap/slab memory or cross VM, IOMMU, or container-to-host security boundaries.
- C:HConfidentiality impact, high
- The kernel performs an out-of-bounds 8-byte write past the declared bpf_attr size; per CNA guidance any such memory corruption can be leveraged for information disclosure via adjacent userspace secrets, not merely a bounded metadata leak.
- I:HIntegrity impact, high
- The unconditional copy_to_user of query.revision at offset 56 when size is below offsetofend(revision) is an out-of-bounds write of up to 8 bytes (revision value partly influenced by prior cgroup BPF attach/detach), enabling userspace heap/stack corruption and potential code execution.
- A:HAvailability impact, high
- The OOB write can crash or hang privileged BPF/cgroup management daemons (containerd, Cilium, kubelet) still issuing legacy-sized BPF_PROG_QUERY after a 6.17+ upgrade, and malicious CAP_NET_ADMIN callers can repeatedly corrupt adjacent mappings to induce process termination.