CVE-2015-1333

What it actually does

Local memory leak in the keyring subsystem where repeated add_key calls referencing existing keys fail to release allocated structures, leading to unbounded kernel memory consumption and eventual denial of service.

Why it matters to the business

Local users on affected Linux systems can exhaust kernel memory, causing system instability, degraded performance, or crashes that interrupt workloads and require reboots; low exploitability limits widespread impact but still necessitates patching on any exposed hosts.

How an attack unfolds

An attacker with local shell access writes a small program or script that repeatedly invokes the add_key system call against the same existing key, triggering the leak in __key_link_end on each iteration until memory pressure forces the kernel to terminate processes or panic.

How to fix it

Upgrade the Linux kernel to version 4.1.4 or newer; rebuild and reboot with the patched kernel; apply vendor backports where available for long-term supported distributions.

How to confirm the fix worked

Verify running kernel version is 4.1.4 or later; confirm the __key_link_end function no longer leaks by inspecting source or applying memory-leak test workloads; monitor /proc/meminfo and slabinfo for key_jar growth under load.

Typical attack path

1. Obtain unprivileged local shell access on target Linux host
2. Locate or create a persistent key in the user's keyring
3. Execute a loop of add_key calls referencing that key from user space
4. Monitor system memory until kernel exhaustion occurs

How to detect it

Review system logs for repeated keyring operations coinciding with unexplained memory growth; inspect auditd or eBPF traces of add_key calls from unprivileged users; correlate high slab usage in key_jar with process activity.

What your security team should do

• Prioritize kernel updates on all internet-facing and multi-user systems within standard patch windows
• Restrict local user accounts and consider seccomp or LSM policies to limit keyring syscalls where feasible
• Include kernel version checks in vulnerability scanning and asset inventory
• Monitor for unusual memory growth correlated with keyctl or add_key activity in production workloads