CVE-2015-3246Red Hat Libuser Race Condition Vulnerability

Patch nowHigh7.4ExploitedEPSS 8.5%

CVE-2015-3246 is a time-of-check to time-of-use race in Red Hat Libuser, rated high (7.4 on CVSS 3.1).

Why this priority: Exploited in the wild: listed in CISA's KEV catalog.

Published 11 Aug 2015 · Updated 2 Oct 2026 · NVD status: Analyzed

What it is

Something is checked, then changed by an attacker before it is used. Permissions or privileges are not enforced as intended.

How it is reached

An attacker can exploit it by someone who can already run code or sign in on the machine, without an account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.

What an attacker gains

A successful attack can read the data it protects, change data or behaviour and take it offline. In practice, this kind of flaw lets an attacker win a timing window to bypass a check or corrupt shared state.

Is it being exploited?

CISA added it to the Known Exploited Vulnerabilities catalog on 2026-08-26: it is being exploited in the wild. EPSS estimates a 8.5% chance of exploitation activity in the next 30 days, higher than 95% of scored CVEs.

What to do

Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2026-09-09.
Upgrade Red Hat Libuser to a fixed version for your release line (0.56.13-8, 0.60-7).
Limit who can run code or sign in on the hosts that run it.
Check exposed instances for signs of compromise, not only for the version.

Description from NVD

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.

CVSS: High7.4v3.1reporterCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
High7.2v2.0NVDAV:L/AC:L/Au:N/C:C/I:C/A:C
Fixed in: Libuser: 0.56.13-8, 0.60-7
CISA KEV: Added 26 Aug 2026; federal due date 9 Sept 2026.CISA’s 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.
EPSS: 8.5% chance of exploitation activity in 30 days; higher than 95% of CVEs (10 Nov 2026).
CISA assessment (SSVC): Exploitation: active · Automatable: no · Technical impact: total
Weaknesses: CWE-264 Permissions and access control
CWE-367 Time-of-check to time-of-use race
Affects: Red Hat Libuser
Redhat Enterprise Linux
Opensuse Opensuse
Libuser Project Libuser

What this means for your architecture.

A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.

Components it touches

Operating systems on servers, workstations or devices. Everything on the host inherits the flaw.
Request handlers and jobs that share state. The flaw sits between concurrent requests or processes.
Permission checks in APIs and admin surfaces. The flaw sits between one role or tenant and another.
Multi-tenant services. The flaw sits between one role or tenant and another.

Trust boundaries in play

Host boundary. The attacker needs a foothold on the machine first; the flaw turns a small foothold into a bigger one.
Between concurrent requests or processes. An attacker who crosses it can win a timing window to bypass a check or corrupt shared state.
Between one role or tenant and another. An attacker who crosses it can reach data or actions their role should not allow.

Questions to answer about your own systems

Where does Red Hat Libuser run in your systems, and at which version?
Which of those hosts also run code or users you do not fully trust?
What can it reach once compromised: which data stores, secrets and services?

See how Veriom maps an architecture Take the interactive tour

Advisories

Exploits and proofs of concept

www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt

Sources

CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.