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FreeBSDOperating system

CVE-2026-39461

HIGH · 8.8 CVSS v3.1 Published 2026-05-21
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
libcasper(3) communicates with helper processes via UNIX domain sockets, and uses the select(2) system call to wait for data to become available. However, it does not verify that its socket descriptor fits within select(2)'s descriptor set size limit of FD_SETSIZE (1024). An attacker able to cause an application using libcasper(3) to allocate large file descriptors, e.g., by opening many descriptors and executing a program which is not careful to close them upon startup, may trigger stack corruption. If the target application runs with setuid root privileges, this could be used to escalate local privileges.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

libcasper(3) fails to validate that socket descriptors are within select(2)'s FD_SETSIZE limit (1024) before using select(). An attacker who can cause a vulnerable application to allocate large file descriptors can trigger stack corruption. If the target application runs setuid root, this can lead to local privilege escalation.

MitigationEither patch libcasper to validate descriptor limits before calling select(), or ensure any setuid applications using libcasper properly close file descriptors at startup and do not run with elevated privileges.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FreeBSDOperating system
Affected:= 14.3= 14.4= 15.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the FreeBSD version
    Run 'freebsd-version -k' or 'uname -r' to determine the installed FreeBSD release
    Affected if The version is 14.3, 14.4, or 15.0
  2. Locate libcasper library
    Check for the presence of libcasper using 'ls -la /lib/libcasper*' or 'find / -name 'libcasper*' 2>/dev/null'
    Affected if libcasper is installed on the system
  3. Identify setuid binaries using libcasper
    Run 'find / -perm -4000 -exec ldd {} \; 2>/dev/null | grep -i casper' to find setuid programs linked against libcasper
    Affected if Any setuid root binaries are linked to libcasper
  4. Check current file descriptor usage
    Run 'ulimit -n' to see the current file descriptor limit, and 'ls -1 /proc/self/fd | wc -l' (or equivalent) to count open descriptors
    Affected if The number of open file descriptors approaches or exceeds 1024 while using libcasper-based services

The environment is affected if running FreeBSD 14.3, 14.4, or 15.0 with libcasper present and any setuid programs linked against it, or if file descriptors can accumulate beyond FD_SETSIZE while using libcasper services.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Either patch libcasper to validate descriptor limits before calling select(), or ensure any setuid applications using libcasper properly close file descriptors at startup and do not run with elevated privileges.

Recommended fix Moderate confidence

Apply the relevant FreeBSD security patch for this vulnerability when released; for point releases, upgrade to the latest patched revision of your current branch (14.3-STABLE, 14.4-STABLE, or 15.0-STABLE)

  1. Check the current FreeBSD version using: uname -r
  2. Monitor FreeBSD security advisories at security.freebsd.org for the corresponding security patch (likely FreeBSD-SA-26:XXX)
  3. If a security patch is available, obtain it and apply it according to FreeBSD's patch application instructions
  4. After patching, rebuild any applications linked against libcasper(3)
  5. Restart any running services that use libcasper(3) to load the patched library
  6. Verify the fix by confirming the socket descriptor limit is properly handled in libcasper(3)
Caveat Standard FreeBSD security patches typically have minimal risk; ensure adequate testing in non-production environments before deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in FreeBSD Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
19.0 hours of engineering $3,380
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-39461 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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