CVE-2015-3246: Red Hat Libuser

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

Yes, if you run Red Hat Libuser. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-08-26, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-09; treat that as the outer limit, not the target.
EPSS 8.5%, percentile 95: FIRST’s model estimates a 8.5% chance of exploitation activity in the next 30 days, higher than 95% of all scored CVEs (very high). EPSS is a probability, not a verdict.
Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
Editorial verdict: Most can relax. libuser CVE-2015-3246: 2015 Linux Root Bug Lands in KEV — Any RHEL or CentOS 6 or 7 host that has taken updates since July 2015 is already fixed; the real risk is forgotten legacy Linux servers, where this is one of several old root exploits attackers now chain after a web compromise.

What it is

libuser before 0.56.13-8 and 0.60 before 0.60-7, as used in the userhelper program in the usermode package, directly modifies /etc/passwd, which allows local users to cause a denial of service (inconsistent file state) by causing an error during the modification. NOTE: this issue can be combined with CVE-2015-3245 to gain privileges.

CISA’s summary

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.

Weakness type: CWE-367.

Product: Red Hat Libuser · Assigned by: redhat · Published: 2015-08-11

Affected and fixed versions

Vendor	Product	Affected versions (per CVE record)
n/a	n/a	see vendor advisory

Severity scores

Scored by	CVSS	Score	Vector
CISA-ADP	3.1	7.4 High	`CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`

Attack vector: local access needed
Attack complexity: high (needs special conditions)
Privileges required: none (no login)
User interaction: none
Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

CISA KEV: added 2026-08-26; federal due date 2026-09-09. Known ransomware use: Unknown.
CISA required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
CISA SSVC assessment: exploitation active, automatable no, technical impact total.
FIRST EPSS (model of 2026-10-21): 8.50% probability of exploitation activity in the next 30 days; percentile 95.

Timeline

2015-07-23 — erroneo.us brief: libuser CVE-2015-3246: 2015 Linux Root Bug Lands in KEV
2015-08-11 — CVE record published by redhat
2026-08-26 — Added to CISA’s Known Exploited Vulnerabilities catalog
2026-09-09 — CISA remediation deadline for US federal agencies
2026-10-01 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Other references from the CVE record and advisory

76022 securityfocus.com
44633 exploit-db.com
qualys.com qualys.com
1033040 securitytracker.com
blog.talosintelligence.com blog.talosintelligence.com

All exploited Red Hat vulnerabilities · Today’s Security Digest