External risk intelligence

Libuser Local Denial of Service Affecting /etc/passwd

CVE advisoryKnown Exploit

CVE-2015-3246

The vulnerability exists within a local system utility (libuser/userhelper) on Linux systems and requires local access to the operating system to exploit. It is not reachable via a network or the public internet.

Denial of Service

Redhat Enterprise Linux

5.06.07.013.2before 0.56.13-80.60 to before 0.60-7

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability involves a local system utility that can cause inconsistencies in a critical system file, potentially leading to service disruption. While direct exploitation requires local access, it can be combined with another issue to escalate privileges. The primary concern is to confirm if this specific utility is in use and potentially exposed.

Local utility can corrupt system files.
It can be combined for privilege escalation.
Confirm relevance and exposure of the utility.

Attack Path

How an attacker could exploit the issue

A local attacker can gain access to the system and trigger this vulnerability by interacting with the userhelper program. This program directly modifies the /etc/passwd file, and a specific sequence of operations can lead to an inconsistent file state. The vulnerability can result in a denial of service due to data corruption or, when combined with another vulnerability, potential privilege escalation.

Requires local system access.
Userhelper program modifies /etc/passwd.
Denial of service or privilege escalation.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could affect the integrity of user account information on a system. When the `userhelper` program encounters an error during modifications to the `/etc/passwd` file, it can lead to an inconsistent state. This issue is present when local users can interact with the `userhelper` program.

User account data integrity.
Error during file modification.
Denial of service on the system.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability affects the libuser component used in Linux systems, likely managed by infrastructure or platform teams. The immediate priority is to locate all instances of the affected technology, assess their business criticality and exposure, identify the responsible system owner, and then plan remediation actions based on the identified risk.

Identify affected systems and owners.
Verify system criticality and exposure.
Plan risk-based remediation actions.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is libuser?

Libuser is a software library for Linux systems that provides a standard way to manage user and group accounts. It is frequently used by the userhelper program, which helps perform administrative tasks—like changing passwords—in a way that bridges the gap between regular users and system-level configuration files.

What does CVE-2015-3246 mean in plain English?

This vulnerability involves a 'race condition,' which is a timing-related flaw. When the affected software tries to update the system's user database file (/etc/passwd), it can be interrupted in a way that leaves the file corrupted or in an inconsistent state. This weakness falls under categories related to incorrect permission management and race conditions.

How is this vulnerability triggered?

An attacker must already have local access to the system to trigger this bug. The issue occurs when the userhelper program is manipulated to fail during a file modification process. It is not triggered by remote network requests, website traffic, or other external inputs that do not have existing, interactive access to the operating system.

Do I need to worry if my system is not internet-facing?

Halo Surface Signal classifies this issue as internal because it requires local system access. While internet-facing systems are generally at higher risk for many vulnerabilities, this specific flaw focuses on local utility misuse. Even on internal systems, you should still address it because local attackers—or compromised local accounts—could potentially use it to cause service disruption.

How should I respond to CVE-2015-3246?

First, identify if any of your systems are running the affected versions of the libuser package. Once located, verify the importance of those systems to your operations. Coordinate with your infrastructure or platform teams to plan and apply the necessary security updates provided by your Linux distribution vendor to resolve the library flaw.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.