CVE-2026-98862 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
audit: fix exe mark UAF in kill_rules()
kill_rules() removes mixed AUDIT_DIR and AUDIT_EXE rules when an audit tree is pruned. It drops entry->rule.exe before removing the rule from the RCU-visible filter lists.
After a rule has been installed with AUDIT_ADD_RULE, which requires CAP_AUDIT_CONTROL, removing the watched directory can race with another task that is still evaluating the rule. In that case, fsnotify can free the executable mark before the reader reaches audit_mark_compare(), causing a use-after-free.
KASAN reports:
BUG: KASAN: slab-use-after-free in audit_mark_compare+0x8d/0xa0
Unlink the published rules from the RCU-visible lists and retain them on tree->rules for cleanup. If any rule has an executable mark, wait for a single RCU grace period before removing the marks and scheduling the entries for freeing. Otherwise, call_rcu() already provides the required deferred freeing without a synchronous wait.
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel audit subsystem contains a critical use-after-free vulnerability within the kill_rules function, which is responsible for pruning audit trees by removing specific rules such as AUDIT_DIR and AUDIT_EXE entries. This flaw arises from an improper ordering of operations during rule removal, where the executable mark associated with a rule is freed before the rule itself has been safely unlinked from the Read-Copy-Update visible filter lists. The vulnerability specifically impacts scenarios involving mixed audit rules that monitor both directories and executables, creating a race condition between the thread pruning the tree and other concurrent tasks evaluating these rules.
The operational mechanism of this flaw involves the interaction between kernel auditing logic and filesystem notification subsystems. When an administrator with CAP_AUDIT_CONTROL privileges installs a rule using AUDIT_ADD_RULE to watch specific paths or executable files, the system registers marks via fsnotify to track file access events. If a watched directory is subsequently unlinked while other processes are still in the process of evaluating these rules, the filesystem notification layer may free the associated executable mark prematurely. This premature deallocation occurs before the audit subsystem completes its comparison operations within audit_mark_compare, leading directly to a use-after-free condition that can be detected by Kernel Address Sanitizer as a slab-use-after-free error.
From a security perspective, this vulnerability is classified under CWE-416, Use After Free, and aligns with MITRE ATT&CK techniques related to privilege escalation or denial of service through kernel memory corruption. Although the initial trigger requires CAP_AUDIT_CONTROL privileges, which limits direct exploitation by unprivileged users, the resulting use-after-free can potentially be leveraged for local privilege escalation if an attacker can manipulate race conditions or exploit subsequent memory reuse patterns. The impact includes system instability, potential data leakage from freed slab objects, and complete kernel panic due to invalid memory access during rule comparison operations.
The resolution implemented in this patch addresses the root cause by altering the lifecycle management of audit rules within RCU contexts. Instead of immediately dropping the executable mark upon initiating rule removal, the fix ensures that published rules are first unlinked from the RCU-visible lists while being retained on the internal tree structure for safe cleanup. For any rule containing an executable mark, the system now waits for a single RCU grace period before proceeding to remove the marks and schedule entries for freeing. This synchronization delay guarantees that all concurrent readers have completed their access to the data structures involved in audit_mark_compare. Rules without executable marks continue to utilize standard call_rcu deferred freeing mechanisms, maintaining performance efficiency while ensuring memory safety across all rule types.