CVE-2015-3246: Red Hat Libuser Race Condition Vulnerability Actively Exploited (CISA KEV)

CISA has listed CVE-2015-3246, a race condition in Red Hat libuser, as an actively exploited vulnerability. The flaw allows an authenticated local user to corrupt the /etc/passwd file, potentially causing a denial of service or allowing privilege escalation on systems that still run vulnerable code. You can learn more about privilege escalation vulnerabilities in CVE-2015-5287.

The Known Exploited Vulnerabilities designation confirms that exploitation has occurred outside controlled testing. According to the CISA catalog description, the vulnerability affects the way libuser handles changes to account information. A successful exploit can damage the system file used to store core user-account records, with consequences ranging from loss of normal system operation to elevated privileges.

The vulnerability is not described as an unauthenticated remote-access flaw. An attacker must first have authenticated local access, which may come from a legitimate low-privileged account or a separate compromise. That condition narrows the attack surface, but it does not remove the risk: privilege-escalation flaws can help an intruder turn limited access into broader control. For example, see CVE-2022-0995. CISA’s supplied direction is to apply available mitigations.

The notice does not identify a particular malware family, threat group or campaign. It also does not specify which currently deployed product versions remain exposed. Administrators need to compare installed libuser package versions with the security guidance and updates issued for their operating system rather than relying on the vulnerability’s age.

Local Access Can Become Root

CVE-2015-3246 matters because a local foothold is often only one stage of an intrusion. An attacker operating through a restricted account may use a privilege-escalation flaw to reach protected files, administrative functions or other users’ data. Corruption of /etc/passwd can also interfere with authentication and account handling, producing a denial of service even when privilege escalation does not succeed.

The CISA listing gives defenders a reason to move this flaw ahead of vulnerabilities supported only by theoretical proof. Organizations running older Red Hat-derived environments, long-lived servers or systems with delayed patch cycles face the clearest need to check exposure. The development also shows why legacy vulnerabilities remain operational risks when vulnerable packages survive in production.

A 2015 Flaw Resurfaces

CVE-2015-3246 was assigned in 2015 and concerns a race condition, a software error in which the outcome depends on the timing of overlapping operations. In this case, the unsafe behavior can affect changes involving local user-account records. The security impact comes from corruption of a file that is central to Unix and Linux account management.

The vulnerability’s age does not establish whether a given machine is safe. Systems may remain exposed because of unsupported releases, incomplete patching, old appliances or forgotten servers. CISA’s active-exploitation status shifts the issue from a historical software defect to a current defensive priority for organizations that still have affected installations.

“allows authenticated local users to corrupt the /etc/passwd file”

— CISA Known Exploited Vulnerabilities catalog description

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Campaign Scope and Targets Unknown

It is not yet clear who is exploiting CVE-2015-3246, how many systems have been affected or when the observed exploitation began. The supplied CISA information does not describe the initial access method, targeted industries, geographic reach or whether the activity forms part of a coordinated campaign.

The notice also does not establish that every installation of libuser is vulnerable. Exposure depends on the operating-system release, package build and patch status. No information supplied here confirms whether exploitation has caused only account-file corruption or has produced successful privilege escalation in observed incidents.

Patch Checks and Incident Review

Defenders should identify systems running libuser, verify their installed versions against applicable vendor advisories and apply security updates or documented mitigations. Systems that cannot be updated should receive tighter access controls and monitoring while administrators determine a supported remediation path.

Security teams should also review affected hosts for unexpected changes to account records, unexplained authentication failures and unauthorized privilege changes. Future advisories may provide more detail about affected versions, exploitation patterns or threat actors. Until then, the confirmed fact is limited but actionable: CISA has evidence of exploitation, and vulnerable installations require prompt review.

Key Questions

What is CVE-2015-3246?

It is a race condition vulnerability in Red Hat libuser that can allow an authenticated local user to corrupt /etc/passwd, causing service disruption or possible privilege escalation.

Can the flaw be exploited remotely without an account?

The supplied description requires authenticated local access. It does not identify CVE-2015-3246 as a standalone unauthenticated remote exploit, though an attacker could reach it after gaining access through another route.

Why is a vulnerability from 2015 news now?

CISA has classified it as actively exploited. That status means the issue is no longer only historical or theoretical and may threaten unpatched systems still in service.

What should administrators do?

Administrators should check for vulnerable libuser packages, follow operating-system vendor guidance, apply available fixes or mitigations and inspect exposed systems for account-file corruption or unauthorized privilege changes.

Source: kev