CVE-2015-1328

What it actually does

The overlayfs implementation fails to enforce proper permission checks when creating files in the upper filesystem directory within an arbitrary mount namespace, allowing a local process to write files that result in root-owned artifacts and privilege escalation.

Why it matters to the business

Local attackers can obtain full root access on affected Ubuntu systems, leading to complete host compromise, data theft, persistence, and lateral movement with high operational disruption and remediation cost.

How an attack unfolds

An attacker with a local shell creates a new mount namespace, sets up an overlayfs mount pointing a writable upper directory at a privileged location, then leverages the missing permission validation to create or modify files that grant root privileges when executed or referenced by the system.

How to fix it

Upgrade chromium-browser on Ubuntu 14.04 LTS to version 41.0.2272.76-0ubuntu0.14.04.1.1076 or later; apply equivalent kernel and overlayfs fixes from Ubuntu updates; disable untrusted overlayfs mounts via AppArmor or namespace restrictions where upgrades are delayed.

How to confirm the fix worked

Verify package versions match or exceed the listed fixed releases, confirm overlayfs permission checks are present in the running kernel, and test that unprivileged namespace mounts no longer allow unauthorized root file creation.

Typical attack path

1. Obtain unprivileged local shell access
2. Create a new user or mount namespace
3. Prepare overlayfs mount with attacker-controlled upper directory
4. Trigger file creation that bypasses permission checks
5. Escalate to root via resulting privileged artifacts
6. Install persistence or move laterally

How to detect it

Search system logs and audit records for unusual mount namespace creation followed by overlayfs mounts; inspect /proc/*/mountinfo and dmesg for overlayfs activity from non-root users; review file creation timestamps in upper directories of overlay mounts for anomalies.

What your security team should do

• Immediately patch all Ubuntu 14.04 systems to the specified chromium-browser fixed version
• Audit systems for active overlayfs usage in containers or user namespaces
• Restrict unprivileged mount namespaces via kernel parameters or AppArmor profiles
• Monitor EPSS and exploit maturity; prioritize patching given weaponized public exploits
• Review local user accounts and remove unnecessary sudo or namespace capabilities