CriticalCVE-2015-3246

    Red Hat Libuser Race Condition Vulnerability (CVE-2015-3246)

    Published Last modified In CISA KEV since Sources: CVE.org, Ubuntu

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    What is affected, what to do

    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.

    The vulnerability is being actively exploited; treat it as a priority. Update Red Hat Libuser to version 0.56.13-8, Red Hat Libuser to version 0.60-7. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Redhat Enterprise Linux eq 5.0..5.0
    • Redhat Enterprise Linux eq 6.0..6.0
    • Redhat Enterprise Linux eq 7.0..7.0
    • OpenSUSE eq 13.2..13.2
    • Red Hat Libuser lt *..0.56.13-8
    • Red Hat Libuser lt 0.60..0.60-7
    Fixed in
    • Red Hat Libuser 0.56.13-8
    • Red Hat Libuser 0.60-7

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.4

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.4

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org, Ubuntu

    8.5 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 95.1

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    209.29 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.4 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.4
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    8.5 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    95.1
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 27 August 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-367

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This is a local privilege-escalation building block. An attacker first needs a foothold shell, typically from stolen SSH credentials or a webshell, then chains this race condition with CVE-2015-3245 to reach root. Public exploit code has existed for years, and exploitation likelihood sits well above average; CISA does not flag ransomware campaign use. Typical targets are legacy RHEL 6/7 and older openSUSE estates with multiple local users. Fully patched fleets face minimal risk. Legacy multi-user or internet-adjacent hosts should be remediated within days, and removing the setuid bit is an immediate, low-cost bridge until then.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Run rpm -q libuser usermode across all RHEL, CentOS and openSUSE hosts. libuser before 0.56.13-8 and 0.60 before 0.60-7 is vulnerable. Distributions backport fixes, so compare the installed build against the Red Hat or SUSE advisory. Patch available from the vendor — check the vendor advisory for the exact package version.
      • Patch: Apply the update via yum update libuser usermode or zypper patch. Patch CVE-2015-3245 (userhelper/chfn) at the same time, because privilege escalation requires chaining both bugs. No reboot is needed.
      • No-patch stopgap: Strip the setuid bit with chmod u-s /usr/sbin/userhelper. This kills the attack path outright. On servers the impact is usually limited to losing GUI console helpers such as system-config-*.
      • Integrity check of /etc/passwd: Run pwck -r and hunt for unexpected UID 0 accounts with awk -F: '$3==0' /etc/passwd. Diff the file against /etc/passwd- or your AIDE baseline, and look for truncated or malformed lines.
      • Order by multi-user exposure: Start with jump hosts, terminal servers, shared developer and build boxes, and shell hosts. Next, fix systems where a web application compromise would hand an attacker a local shell.

    2. Runbook step 2

      Mitigation layers

      • Configuration (filesystem): Inventory SUID binaries (find / -perm -4000 -type f 2>/dev/null) and check them against an allowlist. On servers that do not need them, permanently neuter userhelper, chfn and chsh.
      • IAM/least privilege: Cut interactive shell access to what operations actually require. Set service accounts to /sbin/nologin. Restrict SSH to admin groups via AllowGroups, since exploitation requires local code execution.
      • Endpoint hardening: Keep SELinux enforcing on RHEL 7 and later. Limit userhelper use through PAM (/etc/pam.d/chfn, /etc/pam.d/chsh) with pam_wheel or pam_succeed_if, so only authorised groups can invoke it.
      • File integrity monitoring: Enable AIDE, Tripwire or EDR FIM on /etc/passwd, /etc/shadow and /etc/group. Alert on any change outside a change window.
      • Backup and recovery: Keep off-host copies of /etc/passwd and /etc/shadow. A corrupted passwd file means login outages, so document the rescue-console recovery path.

    3. Runbook step 3

      Detection rules

      • auditd, userhelper execution: -a always,exit -F path=/usr/sbin/userhelper -F perm=x -F auid>=1000 -F auid!=unset -k userhelper_exec. SPL: index=linux key=userhelper_exec | stats count values(exe) by host, auid. On servers, any hit warrants a look.
      • auditd, passwd writes: -w /etc/passwd -p wa -k passwd_mod. Alert when exe=/usr/sbin/userhelper writes the file on behalf of a non-admin auid, or when writes arrive in rapid bursts that suggest race attempts.
      • Resource-limit tampering: The public exploit forces write errors through file-size limits. Correlate setrlimit/prlimit64 syscalls (-a always,exit -F arch=b64 -S setrlimit -S prlimit64 -F auid>=1000 -k rlimit) with a userhelper execution by the same auid shortly afterwards.
      • EDR process ancestry: Flag the chain bash/sh → userhelper → (chfn|chsh) when arguments are odd, such as embedded newlines or oversized GECOS fields. Also flag any euid=0 shell whose ancestry traces back to an unprivileged login.
      • State indicators: Watch for new UID 0 entries, empty password fields (::), a truncated final line in /etc/passwd, or a sudden drop in file size. Schedule an osquery check (SELECT * FROM users WHERE uid=0;) to catch these.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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.

    Source: cvelistv5, Ubuntu Security Notices, NVD (NIST), CISA KEV Catalog

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    libuser_projectlibuser
    • 0.60 – < 0.60-7
    • < 0.56.13-8
    • 0.60-7
    • 0.56.13-8

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxredhatenterprise_linux5.0
    Linuxredhatenterprise_linux6.0
    Linuxredhatenterprise_linux7.0
    Linuxubuntulibuserxenial
    Linuxopensuseopensuse13.2

    Weakness classes (CWE)

    • CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition

      Base

      The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.

      Entry at MITRE CWE-367

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Exploit-DBEDB-ID 44633 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—
    PoC-in-GitHub (nomi-sec)CVE-2015-3246 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. NVD analysis modifiedNVD

    2. Record modifiedCISA ADP

      CVSS V3.1: AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

      CVSS V3.1: before AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H, after —

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
      CVSSremoved
      AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
      —
      SSVC assessmentremoved
      {"id":"CVE-2015-3246","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-26T00:00:00+00:00"}
      —
      SSVC assessmentadded
      —
      {"id":"CVE-2015-3246","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-27T03:56:43.101618Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. CISA KEV entry updated9119a7d8…

      4 individual changes: Date Added, Due Date, Required Action, Vulnerability Name

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Date Addedadded
      —
      2026-08-26
      Due Dateadded
      —
      2026-08-26
      Required Actionadded
      —
      2026-08-26
      Vulnerability Nameadded
      —
      2026-08-26

      Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725

    4. Record modifiedRed Hat

      Show 21 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      http://lists.fedoraproject.org/pipermail/package-announce/2015-August/163044.html
      Referenceadded
      —
      http://lists.fedoraproject.org/pipermail/package-announce/2015-July/162947.html
      Referenceadded
      —
      http://lists.opensuse.org/opensuse-security-announce/2015-08/msg00000.html
      Referenceadded
      —
      http://rhn.redhat.com/errata/RHSA-2015-1482.html
      Referenceadded
      —
      http://rhn.redhat.com/errata/RHSA-2015-1483.html
      Referenceadded
      —
      http://www.securityfocus.com/bid/76022
      Referenceadded
      —
      http://www.securitytracker.com/id/1033040
      Referenceadded
      —
      https://access.redhat.com/articles/1537873
      Referenceadded
      —
      https://www.exploit-db.com/exploits/44633/
      Referenceadded
      —
      https://www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt
      Referenceremoved
      http://lists.fedoraproject.org/pipermail/package-announce/2015-August/163044.html
      —
      Referenceremoved
      http://lists.fedoraproject.org/pipermail/package-announce/2015-July/162947.html
      —
      Referenceremoved
      http://lists.opensuse.org/opensuse-security-announce/2015-08/msg00000.html
      —
      Referenceremoved
      http://rhn.redhat.com/errata/RHSA-2015-1482.html
      —
      Referenceremoved
      http://rhn.redhat.com/errata/RHSA-2015-1483.html
      —
      Referenceremoved
      http://www.securityfocus.com/bid/76022
      —
      Referenceremoved
      http://www.securitytracker.com/id/1033040
      —
      Referenceremoved
      https://access.redhat.com/articles/1537873
      —
      Referenceremoved
      https://www.exploit-db.com/exploits/44633/
      —
      Referenceremoved
      https://www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt
      —
      Reference typeremoved
      https://www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt Types: Exploit
      —

      Source identifier: secalert@redhat.com

    5. Record modifiedCISA ADP

      CVSS V3.1: AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

      CISA assessment (SSVC): exploitation: active, automatable: no

      Weakness type: CWE-367

      Show 5 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
      Weakness type (CWE)added
      —
      CWE-367
      Referenceadded
      —
      https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/
      Referenceadded
      —
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2015-3246
      SSVC assessmentadded
      —
      {"id":"CVE-2015-3246","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-08-26T17:44:11.022663Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Show one older change

    1. Record modifiedCVE Program

      Show 21 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      http://lists.fedoraproject.org/pipermail/package-announce/2015-August/163044.html
      Referenceadded
      —
      http://lists.fedoraproject.org/pipermail/package-announce/2015-July/162947.html
      Referenceadded
      —
      http://lists.opensuse.org/opensuse-security-announce/2015-08/msg00000.html
      Referenceadded
      —
      http://rhn.redhat.com/errata/RHSA-2015-1482.html
      Referenceadded
      —
      http://rhn.redhat.com/errata/RHSA-2015-1483.html
      Referenceadded
      —
      http://www.securityfocus.com/bid/76022
      Referenceadded
      —
      http://www.securitytracker.com/id/1033040
      Referenceadded
      —
      https://access.redhat.com/articles/1537873
      Referenceadded
      —
      https://www.exploit-db.com/exploits/44633/
      Referenceadded
      —
      https://www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt
      Referenceremoved
      http://lists.fedoraproject.org/pipermail/package-announce/2015-August/163044.html
      —
      Referenceremoved
      http://lists.fedoraproject.org/pipermail/package-announce/2015-July/162947.html
      —
      Referenceremoved
      http://lists.opensuse.org/opensuse-security-announce/2015-08/msg00000.html
      —
      Referenceremoved
      http://rhn.redhat.com/errata/RHSA-2015-1482.html
      —
      Referenceremoved
      http://rhn.redhat.com/errata/RHSA-2015-1483.html
      —
      Referenceremoved
      http://www.securityfocus.com/bid/76022
      —
      Referenceremoved
      http://www.securitytracker.com/id/1033040
      —
      Referenceremoved
      https://access.redhat.com/articles/1537873
      —
      Referenceremoved
      https://www.exploit-db.com/exploits/44633/
      —
      Referenceremoved
      https://www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt
      —
      Reference typeremoved
      https://www.qualys.com/2015/07/23/cve-2015-3245-cve-2015-3246/cve-2015-3245-cve-2015-3246.txt Types: Exploit
      —

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

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