CVE-2026-89761

Received Received - Intake

Buffer Overflow in Linux Kernel AppArmor

Publication date: 2026-09-11

Last updated on: 2026-09-11

Assigner: kernel.org

Description

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().

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-11

Last Modified

2026-09-11

Generated

2026-09-12

AI Q&A

2026-09-12

EPSS Evaluated

N/A

NVD

CVE-2026-89761

EUVD

EUVD-2026-76673

Affected Vendors & Products

Vendor	Product	Version / Range
apparmor	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This is a Linux kernel vulnerability where a function called aa_vec_unique() writes a null terminator beyond the allocated space in a vector. The issue occurs because aa_label_strn_parse() sets up a vector without reserving space for the terminator entry. When the vector is full (LOCAL_VEC_ENTRIES) or larger, the terminator writes past the end, causing an out-of-bounds write.

Detection Guidance

This vulnerability is specific to the Linux kernel's AppArmor module and requires local system access to detect. Check if your kernel version includes the fix by running uname -a and comparing against patched versions. Monitor system logs for crashes or errors related to AppArmor or label parsing.

Impact Analysis

An unprivileged user could exploit this to corrupt kernel memory by writing a specially crafted label to /proc/self/attr/apparmor/current or via lsm_set_self_attr(). This could lead to system crashes, privilege escalation, or other security issues depending on the kernel's memory layout.

Mitigation Strategies

Update your Linux kernel to the latest patched version immediately. If immediate updating is not possible, restrict access to /proc/self/attr/apparmor/current and securityfs .access files to prevent unprivileged exploitation. Disable AppArmor if not in use.

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