CVE-2015-3246 is a race condition vulnerability in Red Hat Libuser. CISA added it to the Known Exploited Vulnerabilities catalogue on 26 August 2026, which means attackers have used it in real attacks. Red Hat libuser contains a race condition vulnerability that allows authenticated local users to corrupt the /etc/passwd file to cause a denial of service or privilege escalation.
What a race condition means in a local system component
A race condition exists when two or more operations can reach a shared state in the wrong order. In a system component such as Red Hat Libuser, that timing flaw can turn an ordinary local action into corruption of account data or an unsafe permission change.
For a component that writes identity-related files, the danger is not just a crash. If updates to /etc/passwd are not handled atomically, an attacker may exploit the timing window to alter account records in ways the program did not intend.
Why this vulnerability class is dangerous in account-management software
Libuser sits close to account and password file handling, so a race condition here can affect the integrity of local authentication data. When the vulnerable code is reached by an authenticated local user, the flaw can be used to interfere with file contents that other programs trust.
That makes the issue especially serious in software that mediates user accounts, because the outcome can move from denial of service to privilege escalation. For a broader explanation of why race conditions are a common software weakness class, see the CWE Top 25 Guide, which helps place timing flaws alongside other root-cause weaknesses.
How organisations assess exposure and validate remediation
Exposure checking starts with knowing whether Red Hat Libuser is present anywhere in the environment, then confirming whether any affected host is reachable by users who can trigger the vulnerable path. In practice, that means pairing asset inventory with vendor guidance and exploitation priority data, rather than relying on version guessing alone.
For authoritative vulnerability records and current record details, use the NIST National Vulnerability Database and the CVE Program. For prioritisation and remediation workflow, the Vulnerability Management Guide is useful for mapping KEV-listed issues into asset scope, verification, exceptions, and remediation SLAs.
Because the vulnerability was added to CISA’s KEV catalogue, organisations should treat exposed or business-critical installations as high priority until they are confirmed remediated or covered by compensating controls.
What defenders should look for after exploitation
When a local timing flaw is exploited, the impact may not stop at the initial corruption event. Account-file tampering can create a lasting integrity problem, and in the worst case it can leave the system with unauthorized privilege changes even after the original exploit window is closed.
Post-patch review should therefore look for unexpected edits to local account files, suspicious privilege changes, and any sign that the system was accessed by a local user around the exploitation window. If compromise is suspected, the review should extend to identity material linked to the affected host, including local credentials and any service access that may have been exposed by the altered account state.
Where timing flaws are discussed in the broader weakness literature, the CWE Top 25 Guide is a useful reference point for understanding how race conditions can enable integrity failures that are hard to spot after the fact.
Risk and Threat Considerations
This vulnerability matters because it gives an authenticated local user a path to corrupt a trusted account database. That can produce service disruption at minimum, and in a successful exploitation scenario it can undermine host integrity and privilege boundaries on a system that other controls assume is stable.
Failure mechanism: The attacker exploits a race in file handling so that the application and the underlying filesystem observe state changes in the wrong order, allowing unauthorized modification of /etc/passwd.
Impact: The host may suffer denial of service, account corruption, or privilege escalation, and the resulting trust loss can persist until the account state is verified and repaired.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
CIS Controls v8 and NIST SP 800-53 Rev 5 set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-2 — Software Inventory | Tracks where vulnerable software exists across hosts and systems |
| Recommendation — Inventory systems running the vulnerable component and prioritise them for remediation. | ||
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | Requires timely remediation of identified software flaws |
| SI-7 — Software, Firmware, and Information Integrity | Protects critical files and states from unauthorized modification | |
| AU-2 — Event Logging | Supports detection and review of suspicious local activity around exploit windows | |
| Recommendation — Apply flaw remediation processes to remove or mitigate the vulnerable libuser release. Verify account-file integrity and detect unauthorized changes after patching. Log and review local account-management activity around the suspected exploitation window. | ||
| ISO/IEC 27001:2022 | A.8.8 — Management of technical vulnerabilities | Requires identifying and remediating technical vulnerabilities in assets |
| Recommendation — Track the CVE as a technical vulnerability and ensure remediation is recorded and verified. | ||
Practitioner Guidance
Why practitioners should care: Treat account-file race conditions as integrity issues, not just reliability bugs. If the vulnerable component touches identity or privilege records, even a local exploit can become a host-level security event.
What to watch for: Prioritise hosts where the software is exposed to local users, shared administrative workflows, or automation that can reach the vulnerable code path. After remediation, verify account-file integrity and confirm that no unexpected privilege state remains on the system.