Local privilege escalation via unchecked select descriptor
Published May 21, 2026 · Updated May 21, 2026
Stack-based buffer overflow in FreeBSD libcasper allows local users to corrupt stack memory through high socket descriptors. The library passes a socket descriptor of 1024 or greater to FD_SET on a stack-allocated fd_set without checking FD_SETSIZE, causing an out-of-bounds write. Exploitation requires control over inherited file descriptors in a libcasper-using process; a setuid-root target turns the corruption into local privilege escalation.
Summary
What happened
Stack-based buffer overflow in FreeBSD libcasper allows local users to corrupt stack memory through high socket descriptors. The library passes a socket descriptor of 1024 or greater to FD_SET on a stack-allocated fd_set without checking FD_SETSIZE, causing an out-of-bounds write. Exploitation requires control over inherited file descriptors in a libcasper-using process; a setuid-root target turns the corruption into local privilege escalation.
The record
- CVE
- CVE-2026-39461
- Published
- May 21, 2026
- Updated
- May 21, 2026
- Vendor
- The FreeBSD Project
- Product
- FreeBSD
- Classifications
- CWE-121, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- May 21, 2026CVE publishedPublication date reported by the CVE source.
- May 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=14.3-RELEASE <p14
- Affected versionversion=14.4-RELEASE <p5
- Affected versionversion=15.0-RELEASE <p9
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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