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FreeBSDOperating system

CVE-2026-39457

HIGH · 7.8 CVSS v3.1 Published 2026-04-30
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
80/100
Remediation priority · High
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
When exchanging data over a socket, libnv uses select(2) to wait for data to arrive. However, it does not verify whether the provided socket descriptor fits in select(2)'s file descriptor set size limit of FD_SETSIZE (1024). An attacker who is able to force a libnv application to allocate large file descriptors, e.g., by opening many descriptors and executing a program which is not careful to close them upon startup, can trigger stack corruption. If the target application is setuid-root, then this could be used to elevate 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

libnv uses select(2) to wait for socket data without validating that the socket descriptor is within FD_SETSIZE (1024). When file descriptors exceed this limit, the fd_set structure overflows, causing stack corruption. On setuid-root applications, this enables local privilege escalation.

MitigationUpgrade libnv to a version that validates socket descriptors against FD_SETSIZE or refactor to use poll(2)/epoll(7) which lack this limitation.

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:= 13.5= 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
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/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 base system version
    Run 'uname -r' or check /etc/os-release to determine the installed FreeBSD version
    Affected if The version is 13.5, 14.3, 14.4, or 15.0
  2. Determine if libnv is in use
    Identify applications or services that depend on libnv by checking library dependencies with 'ldd' on binaries or reviewing installed packages that may link against libnv
    Affected if Any application or service built against the system libnv library is in use on an affected FreeBSD version
  3. Verify if the application using libnv is setuid-root
    Check the permissions of binaries that depend on libnv using 'ls -la /path/to/binary' to see if the setuid bit is set (indicated by 's' in the owner permissions)
    Affected if A setuid-root binary that links to libnv is present and executable on the system
  4. Check current file descriptor usage
    Run 'ulimit -n' to see the current file descriptor limit, and 'procstat -f <pid>' or 'ls /proc/<pid>/fd' (if procfs is mounted) to count open file descriptors for processes using libnv
    Affected if The process using libnv has more than 1024 file descriptors open (exceeding FD_SETSIZE) while running as setuid-root on an affected version
  5. Inspect for stack corruption indicators
    Review system logs, audit logs, and core dumps (if generated) for signs of stack corruption or crashes affecting binaries that use libnv
    Affected if Unexplained crashes or memory corruption occurs in setuid-root processes that depend on libnv on an affected FreeBSD version

A system is affected if it runs FreeBSD 13.5, 14.3, 14.4, or 15.0 with a setuid-root application using libnv that has more than 1024 file descriptors open, causing select(2) to overflow the fd_set structure.

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

Upgrade libnv to a version that validates socket descriptors against FD_SETSIZE or refactor to use poll(2)/epoll(7) which lack this limitation.

Recommended fix Moderate confidence

FreeBSD 15.1 or latest stable branch (15-STABLE)

  1. Identify all setuid-root programs or daemons on the system that link against libnv by running: find / -perm -4000 2>/dev/null
  2. Check which of these programs handle network sockets by reviewing their functionality or source code
  3. If vulnerable setuid programs exist, temporarily remove the setuid bit until patched: chmod -s /path/to/program
  4. Alternatively, limit the maximum number of open file descriptors for vulnerable processes using ulimit -n or resource limits
  5. Monitor for any FreeBSD security advisories at security.freebsd.org for the official patch
Caveat Upgrading FreeBSD base system carries standard upgrade risks; test in staging environment first

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

Fix this in FreeBSD Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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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-2026-39457 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
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  • Version or environment caveats, and links to real fixes
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