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CVE-2026-72427
bpf: Fix effective prog array index with BPF_F_PREORDER
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem kernel/bpf. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72427 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 | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| 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
replace_effective_prog() and purge_effective_progs() located the slot in the effective array by walking the program hlist and counting entries linearly. That count does not match the array layout: compute_effective_ progs() places BPF_F_PREORDER programs at the front (ancestor cgroup first, attach order within a cgroup) and the rest after them (descendant cgroup first). So when a preorder program is present, the linear hlist position no longer equals the program's index in the effective array. For replace_effective_prog() (bpf_link_update()) this overwrote the wrong slot, corrupting the effective order. For purge_effective_progs(), it could dummy out a slot belonging to a different program and leave the detached program in the array while bpf_prog_put() drops its reference, i.e. a use-after-free. Fix both by replaying compute_effective_progs()'s placement (including the per-cgroup preorder reversal) in a shared effective_prog_pos() helper. Identify the entry by its struct bpf_prog_list pointer rather than by (prog, link) value, so the lookup resolves to exactly the attachment the syscall selected even when the same bpf_prog is attached to several cgroups in the hierarchy.
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.
kernel/bpf/cgroup.c
- What this is
- BPF [GENERAL] (Safe Dynamic Programs and Tools)MAINTAINERS section matched on kernel/bpf/ · bpf@vger.kernel.org · Supported
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
- 0.17%, higher than 6.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- kernel/bpf
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.6.93 | 6.6.145 | 525e408c27ae |
| 6.12.31 | 6.12.97 | 41b4320b84fd |
| 6.15 | 6.18.40 | 9697db03e010 |
| 6.15 | 7.1.5 | b584f107ab90 |
| 6.15 | 7.2 | f08aaee3152d |
| 6.14.9 | 0 | 0 |
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
- Exploitation requires local bpf() syscalls (BPF_LINK_CREATE/BPF_PROG_ATTACH with BPF_F_PREORDER, BPF_LINK_UPDATE, BPF_PROG_DETACH/BPF_LINK_DETACH) through __cgroup_bpf_replace/__cgroup_bpf_detach in kernel/bpf/cgroup.c; per kernel CNA guidance BPF cgroup hooks are Local even when later triggered by packets.
- AC:LAttack complexity, low
- Attacker fully controls cgroup hierarchy, BPF_F_PREORDER|BPF_F_ALLOW_MULTI attachments, and bpf_link_update/detach timing; purge_effective_progs UAF needs update_effective_progs() OOM which attacker can induce via memory pressure/large hierarchies, and bpf_link_update ordering corruption triggers without OOM.
- PR:LPrivileges required, low
- Reaching the bug requires CAP_BPF (and CAP_NET_ADMIN for most cgroup BPF types) plus cgroup v2 attach access, commonly obtainable by unprivileged users via delegated cgroups or user namespaces (CAP_BPF/CAP_NET_ADMIN), not init-namespace root.
- UI:NUser interaction, none
- Attacker loads, attaches, and updates/detaches their own cgroup BPF programs and links via bpf(); no separate victim or administrator action is required.
- S:UScope, unchanged
- The bug corrupts kernel cgroup BPF effective-prog arrays causing UAF/ordering corruption within the same kernel security domain, enabling local privilege escalation rather than crossing VM, IOMMU, or sandbox boundaries.
- C:HConfidentiality impact, high
- purge_effective_progs() can leave a detached bpf_prog pointer in the RCU-protected effective array while bpf_prog_put() frees it, yielding a use-after-free read when __cgroup_bpf_run_filter_* later executes the stale program under RCU.
- I:HIntegrity impact, high
- UAF of bpf_prog objects enables heap reuse for arbitrary kernel writes/control-flow hijack; bpf_link_update() mis-indexing can overwrite another attachment's effective slot so attacker-controlled BPF runs in place of security/filter programs on traffic for the whole cgroup tree.
- A:HAvailability impact, high
- Freed-but-still-referenced programs are executed from softirq/network cgroup hooks and reliably cause kernel oops/panic/KASAN failures; ordering corruption can also crash or hang filtering paths serving container/cloud workloads.