CVE-2026-45893: Linux Kernel Privilege Escalation Flaw

CVE-2026-45893 Overview

CVE-2026-45893 is a Linux kernel vulnerability in the AppArmor Linux Security Module. The flaw resides in the policy table creation routine, which processes source blobs that may originate from userspace. These blobs can be unaligned in memory, causing unaligned memory accesses during table construction. On architectures that do not transparently handle unaligned access, this can lead to undefined behavior, kernel faults, or incorrect policy loading. The upstream fix both corrects the unaligned access and optimizes the copy path to avoid the underlying issue.

Critical Impact
A local user able to load AppArmor policy data can trigger unaligned memory access in the kernel, potentially affecting kernel stability on architectures sensitive to alignment.

Affected Products

Linux kernel (mainline) containing the AppArmor policy table creation code
Linux distributions shipping affected stable kernel branches prior to the referenced fix commits
Systems with AppArmor enabled and policy loading permitted

Discovery Timeline

2026-05-27 - CVE-2026-45893 published to the National Vulnerability Database (NVD)
2026-05-27 - Last updated in the NVD database

Technical Details for CVE-2026-45893

Vulnerability Analysis

The vulnerability exists within the AppArmor Linux Security Module (LSM) in the Linux kernel. AppArmor uses serialized policy blobs to construct in-kernel lookup tables that enforce mandatory access control decisions. The table creation logic processes a source blob that may be supplied from userspace via policy load operations. Because the blob's layout does not guarantee natural alignment for the types being read, the original code performs memory accesses on potentially unaligned addresses.

On architectures such as certain ARM, MIPS, and SPARC variants, unaligned accesses can raise CPU exceptions or be handled by slow trap-and-emulate fixups. The fix rewrites the copy path to use alignment-safe primitives, eliminating direct dereferences of unaligned pointers and improving performance on the affected path. The fix is recorded across multiple stable kernel commits, including 226c3b10aab2, 47e351dfef60, 6fc367bfd4c8, and e027999049c4.

Root Cause

The root cause is improper handling of alignment assumptions in the AppArmor table construction code. The implementation accessed multi-byte fields directly from a byte-oriented blob whose offsets were not guaranteed to satisfy the natural alignment of those fields. This constitutes a kernel-level alignment defect closely related to a boundary condition error in input parsing.

Attack Vector

The attack vector is local. A privileged process capable of loading AppArmor policy, typically requiring CAP_MAC_ADMIN, can submit a crafted policy blob whose internal offsets force unaligned reads during table construction. The vulnerability is not remotely reachable and does not require network access. The Exploit Prediction Scoring System (EPSS) probability is very low, consistent with a stability-oriented kernel hardening fix rather than a directly weaponizable flaw.

No public proof-of-concept code is available. Refer to the upstream commits linked in the references for the precise code paths and patch contents.

Detection Methods for CVE-2026-45893

Indicators of Compromise

Kernel log messages referencing alignment traps or Unable to handle kernel paging request originating from AppArmor symbols such as aa_unpack or related table creation functions.
Unexpected AppArmor policy load failures recorded in auditd logs with subject context apparmor="STATUS".
Kernel oops or panic traces with backtraces in AppArmor unpack and table construction routines.

Detection Strategies

Inventory kernel build versions across Linux fleets and compare against the fix commits 226c3b10aab2, 47e351dfef60, 6fc367bfd4c8, and e027999049c4 to identify unpatched hosts.
Monitor audit logs for unusual AppArmor policy load attempts, particularly from non-package-manager processes or unexpected users with CAP_MAC_ADMIN.
Correlate kernel ring buffer entries (dmesg) referencing AppArmor with crash reports or system instability events.

Monitoring Recommendations

Enable auditd rules to capture all apparmor_parser invocations and policy load syscalls.
Forward dmesg and kernel crash dumps to a central logging system to identify alignment exceptions in AppArmor code paths.
Track package versions for linux-image-* and equivalent across distributions to ensure stable kernels include the referenced commits.

How to Mitigate CVE-2026-45893

Immediate Actions Required

Update affected systems to a Linux kernel that includes one of the fix commits referenced in the upstream stable tree.
Restrict the CAP_MAC_ADMIN capability to trusted administrative processes only, preventing unprivileged users from loading AppArmor policy.
Audit existing AppArmor policy loading workflows and ensure they originate from trusted package sources.

Patch Information

The fix is available in the upstream Linux stable tree. Reference the following commits for the corrected AppArmor table creation logic: Kernel Git Commit Fix, Kernel Git Commit Update, Kernel Git Commit Patch, and Kernel Git Commit Change. Apply distribution updates as they become available from Debian, Ubuntu, Red Hat, SUSE, and other vendors.

Workarounds

On architectures that handle unaligned access transparently (such as x86_64), the practical impact is limited; nonetheless, applying the patch is recommended.
Limit AppArmor policy load operations to package-managed workflows and avoid loading untrusted, hand-crafted policy blobs.
Where feasible on alignment-sensitive architectures, consider deferring kernel upgrades that introduce the affected code until the fix is integrated.

bash

# Verify running kernel version and AppArmor status
uname -r
aa-status

# Restrict who can load AppArmor policy by auditing CAP_MAC_ADMIN holders
getcap -r / 2>/dev/null | grep mac_admin

# Apply distribution kernel updates (example: Debian/Ubuntu)
sudo apt update && sudo apt upgrade linux-image-$(uname -r | cut -d- -f3-)
sudo reboot