CVE-2026-89761
massOut-of-bounds write in Linux kernel AppArmor label parsing allows local privilege escalation
The Linux kernel's AppArmor LSM writes a null-terminator pointer one entry past the end of a label vector when parsing a label name: aa_label_strn_parse() sizes its vector via vec_setup() without reserving room for the terminator that aa_vec_unique() writes at vec[n], corrupting memory whenever a label contains LOCAL_VEC_ENTRIES or more '//&'-separated components. An unprivileged local user can trigger this by writing a crafted label name to /proc/self/attr/apparmor/current, via lsm_set_self_attr(2), or through the world-readable/writable securityfs .access file (mode 0666), since the name is parsed before (or entirely without) a permission check. Each component must resolve to a loaded profile, so the target must have AppArmor enabled with policy loaded — the default on Ubuntu, Debian, and SUSE. Successful exploitation corrupts adjacent kernel memory and can plausibly lead to kernel-level code execution and full privilege escalation (CVSS 3.1: 7.8, AV:L/PR:L with high confidentiality, integrity, and availability impact). No public proof of concept exists, the flaw is not in the CISA KEV catalog, and no in-the-wild exploitation is known.
What to do: Apply distribution kernel updates containing the upstream AppArmor fix (which reserves the terminator entry in vec_setup()/DEFINE_VEC()) and reboot, as this is the only complete remediation. Until patched, limit local unprivileged shell access on AppArmor hosts and audit systems carrying many loaded profiles, since a longer policy set makes the overflow easier to reach. Monitor for writes to /proc/self/attr/apparmor/current or securityfs .access containing unusually long '//&'-joined label strings, which are indicators of trigger attempts.
| Linux kernel (AppArmor LSM) | — |
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
In the Linux kernel, the following vulnerability has been resolved: apparmor: fix out-of-bounds write when null terminating a label vec aa_vec_unique() null terminates at vec[n - dups] when VEC_FLAG_TERMINATE is passed. If the components are all distinct no duplicates are dropped, dups is 0 and the terminator goes to vec[n], so the caller has to provide room for n + 1 entries. aa_label_strn_parse() sets up its vector with vec_setup(profile, vec, len, gfp) and then calls aa_vec_unique(vec, len, VEC_FLAG_TERMINATE), but vec_setup() does not reserve the terminator entry. Up to LOCAL_VEC_ENTRIES it uses the local array of LOCAL_VEC_ENTRIES pointers, above that it allocates exactly len pointers. The terminator therefore lands one entry past the end of the local array when len is LOCAL_VEC_ENTRIES, and one entry past the end of the allocation when len is larger. len comes from the number of "//&" separated components in the label name and label_count_strn_entries() does not bound it. An unprivileged task reaches the parse by writing to /proc/self/attr/apparmor/current or through lsm_set_self_attr(2), both of which go through do_setattr(), and the name is parsed before the change_profile permission is checked. The query_label() path behind the securityfs .access file, which is mode 0666, performs no permission check at all. Every component has to resolve to a loaded profile, so a system with policy loaded is required. The other two VEC_FLAG_TERMINATE users work on a label vec that aa_label_alloc() has already sized with "+ 1 for null terminator entry on vec". Reserve the same entry in vec_setup() and DEFINE_VEC(). Passing len + 1 from the caller instead would move len == LOCAL_VEC_ENTRIES out of the local array and into kzalloc().
- Vector
- CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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