CVE-2026-46328 Overview
CVE-2026-46328 affects the Linux kernel's AppArmor subsystem. The flaw involves incorrect handling of resource limits (rlimit) for POSIX CPU timers. Setting the rlimit value alone does not propagate the limit to POSIX CPU timers, which require an additional step to be updated correctly. The upstream fix refactors the AppArmor code to clarify when the limit is being set and conditionally updates POSIX CPU timers as needed. Severity has not been assigned by NVD at the time of publication, and no public exploit is available.
Critical Impact
Incorrect enforcement of CPU time rlimit values through AppArmor policy may allow processes to exceed intended CPU time constraints until the kernel is patched.
Affected Products
- Linux kernel (AppArmor Linux Security Module)
- Distributions shipping affected upstream kernel versions
- Systems enforcing AppArmor profiles that set CPU time rlimit
Discovery Timeline
- 2026-06-09 - CVE-2026-46328 published to NVD
- 2026-06-09 - Last updated in NVD database
Technical Details for CVE-2026-46328
Vulnerability Analysis
The issue resides in the AppArmor Linux Security Module (LSM), which can apply resource limits to confined processes through its policy language. AppArmor sets the rlimit value but does not perform the additional step required to update POSIX CPU timers. As a result, the configured CPU time limit may not be enforced through the timer path, weakening policy guarantees for confined workloads.
The fix refactors the relevant AppArmor code to separate the act of setting the rlimit from the act of activating it for POSIX CPU timers. After the patch, the kernel conditionally updates POSIX CPU timers whenever the limit is changed by AppArmor, restoring expected behavior.
This is a kernel-level enforcement bug rather than a remote attack primitive. It is best categorized as an Improper Access Control / configuration enforcement issue impacting CPU resource limits.
Root Cause
The root cause is missing logic in AppArmor's rlimit setting path. POSIX CPU timers maintain internal state derived from the process rlimit, and that state must be refreshed when the limit changes. The original AppArmor code updated the limit value but did not invoke the timer update, leaving timers operating against stale limits.
Attack Vector
No network-based attack vector is described. A local process confined by an AppArmor profile that sets CPU time rlimit may continue to consume CPU time beyond the configured ceiling because POSIX CPU timers are not refreshed. The vulnerability does not provide code execution or privilege escalation. It is a policy enforcement weakness.
No verified exploit code is publicly available. Technical details are documented in the upstream Linux kernel stable commits referenced by NVD, including commit 1f736dfe27c8 and commit 2232d7cd2438.
Detection Methods for CVE-2026-46328
Indicators of Compromise
- No published indicators of compromise are associated with CVE-2026-46328.
- The issue is a policy enforcement gap, not a malware or intrusion artifact.
Detection Strategies
- Inventory kernels running AppArmor and compare versions against the patched stable commits listed by NVD.
- Review AppArmor profiles that set RLIMIT_CPU and validate enforcement by running test workloads that intentionally exceed configured CPU time.
- Correlate process CPU consumption with AppArmor policy expectations using host telemetry to identify processes exceeding their declared CPU rlimit.
Monitoring Recommendations
- Monitor kernel package versions across the fleet and alert on hosts running unpatched Linux kernels with AppArmor enabled.
- Track audit logs from AppArmor (/var/log/audit/audit.log or dmesg) for unexpected behavior in profiles using resource limits.
- Track long-running processes that should be bound by RLIMIT_CPU and validate that POSIX CPU timer signals (SIGXCPU) are delivered as expected.
How to Mitigate CVE-2026-46328
Immediate Actions Required
- Apply the upstream Linux kernel patches referenced in the NVD entry for CVE-2026-46328.
- Update distribution kernels through vendor package managers as patched builds become available.
- Audit AppArmor profiles that rely on RLIMIT_CPU and document workloads where CPU time enforcement is security-relevant.
Patch Information
The fix is delivered through multiple Linux kernel stable tree commits, including 1f736dfe27c8, 2232d7cd2438, 28aa93fcfb33, 57d51d41b90e, 6ca56813f4a5, 9bf1fa150775, e1cc11550b2f, and e43818b16815. The change refactors AppArmor's rlimit code and conditionally updates POSIX CPU timers when limits change.
Workarounds
- Enforce CPU resource limits through alternative mechanisms such as systemd CPUQuota= or cgroup v2 cpu.max until kernels are patched.
- Avoid relying solely on AppArmor RLIMIT_CPU for security-critical CPU time enforcement on unpatched kernels.
- Restrict the ability of untrusted users to launch long-running confined workloads where CPU time enforcement is required.
# Verify installed kernel and check for AppArmor status
uname -r
sudo aa-status
# Example: enforce CPU time using systemd as a workaround
sudo systemctl set-property myservice.service CPUQuota=20%
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
