Yes. CISA added CVE-2015-3246 to its Known Exploited Vulnerabilities catalogue on 26 August 2026, which it does only when there is reliable evidence of active exploitation. CISA has not linked it to known ransomware campaigns. 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.
How to verify whether CVE-2015-3246 is active in your environment
The first job is exposure confirmation, not patch panic. Treat this as an authenticated local-privilege issue on systems that use Red Hat libuser, and verify whether the package is installed, whether the host is still within the vulnerable operating range, and whether any local users or automation paths can reach the affected code path under production conditions.
Because CISA has placed the vulnerability in KEV, you should treat it as an exploit-in-the-wild problem and prioritize systems where local access already exists or could be reached through a weaker account. That means checking multi-user servers, jump hosts, build systems, and any environment where local accounts or delegated admin workflows are common.
When a vulnerability is in KEV, version lookups alone are not enough. Confirm the actual package provenance and backported-fix status from the vendor advisory and the KEV catalogue rather than relying on generic package naming, because enterprise Linux distributions often backport fixes without changing the upstream version string.
What the race condition changes operationally
This flaw is not just a denial-of-service defect. The direct answer already states the important consequence: an authenticated local user may corrupt /etc/passwd, which can disrupt logins and, in some cases, lead to privilege escalation. That combination makes the issue materially different from a low-impact local crash because it can alter a core authentication file.
The practical concern is that the vulnerable action targets a shared system identity store. If an attacker can influence /etc/passwd, the result can range from service disruption to unauthorized privilege gain, depending on timing, filesystem state, and which account records are affected. The security problem is therefore both integrity loss and access expansion.
For teams managing shared Linux hosts, that means the issue should be evaluated as an access-control problem as much as a software bug. A local attacker does not need remote reachability if they can already authenticate, so the real question is which accounts and administrative pathways exist on the host today.
What to do if you cannot remediate immediately
If patching must wait, reduce the number of accounts that can interact with the host and narrow the set of users who can run local administrative tools. In practice, that means tightening shell access, reviewing sudoers exposure, and removing any unnecessary local accounts or automation users that can reach libuser-dependent workflows.
Also increase monitoring for changes to sensitive identity files and for unusual local account activity. If the vulnerable host is business-critical, isolate it from less trusted administrative paths, document the exception, and set a short remediation deadline instead of treating it as a routine deferred patch.
Where the environment is already suspicious, consider post-exploitation checks before and after remediation, because a flaw affecting /etc/passwd can be used either to modify access or to hide in plain sight through account changes. Validate account lists, privileged group membership, and login behavior after the fix is applied.
Risk and Threat Considerations
KEV listing is a strong signal that the flaw is being used against real systems, which makes delayed remediation more dangerous than a typical local bug. The main risk is that any authenticated local foothold can become a stepping stone to service disruption or privilege escalation on hosts that still trust local account state.
Failure mechanism: A race condition in libuser can let two operations overlap in a way that corrupts /etc/passwd, breaking the integrity of local account data and potentially creating or elevating access.
Impact: The host may suffer login failures, administrative disruption, or unauthorized privilege gain, and the compromised account state may persist until the file is repaired and access paths are reviewed.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
MITRE ATT&CK addresses the attack and risk surface, while CIS Controls v8, NIST SP 800-53 Rev 5 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-5 — Account Management | CVE-2015-3246 affects local account integrity and privilege escalation. |
| Recommendation — Review and remove unnecessary local accounts and tighten privileged account use on affected Linux hosts. | ||
| NIST SP 800-53 Rev 5 | IA-5 — Authenticator Management | The flaw can corrupt local account data that supports authentication and access decisions. |
| AC-6 — Least Privilege | The exploit requires authenticated local access and can turn excess local privilege into escalation. | |
| Recommendation — Protect and rotate affected authentication material when account integrity may have been altered. Restrict local and delegated administrative privileges to the minimum needed on exposed systems. | ||
| NIST CSF 2.0 | ID.RA-01 — Asset Vulnerability Identification | The question is about confirming exposure to a known exploited vulnerability. |
| PR.AA-05 — Identity Management, Authentication, and Access Control | The issue can corrupt local access state and alter authorization outcomes. | |
| Recommendation — Identify affected assets and prioritize systems that can still reach the vulnerable code path. Enforce access controls that limit who can perform privileged local operations on the host. | ||
| MITRE ATT&CK | T1068 — Exploitation for Privilege Escalation | The vulnerability can be used to move from local access to higher privilege. |
| Recommendation — Map local exploitation attempts to privilege-escalation detections and investigate unusual account changes. | ||
Practitioner Guidance
What to verify: Confirm whether the host uses Red Hat libuser in a way that is reachable by authenticated local users, and do not assume a generic package inventory is enough to prove safety. On Linux estates with mixed packaging, verify the vendor backport status and not just the upstream version string.
Decision rule: If the system is internet-facing, shared by multiple users, or supports privileged local workflows, treat it as high priority and shorten the remediation window. If you see account anomalies, password-file changes, or unexplained privilege changes, escalate to compromise assessment rather than waiting for the next maintenance cycle.
Practitioner takeaway: For KEV-listed local privilege flaws, the key judgment is whether an attacker already has a foothold on the box. If yes, reduce exposure first, patch second, and assume identity-file integrity may already need validation.
Related resources from NHI Mgmt Group
- Guide: Zero-Day and Exploited Vulnerabilities Guide
- How do you patch or mitigate CVE-2015-3246 (Red Hat Libuser Race Condition)?
- CVE-2015-3246 (Red Hat Libuser Race Condition)
- Is CVE-2015-5287 (Red Hat Automatic Bug Reporting Tool Privilege Escalation) being exploited in the wild?
- Is CVE-2021-25394 (Samsung Mobile Devices Race Condition) being exploited in the wild?
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Reviewed and updated by the NHIMG editorial team on October 19, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org