FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

FreeBSD -- select(2) file descriptor set overflow causes stack overflow

Affected packages
15.0 <= FreeBSD < 15.0_9
14.4 <= FreeBSD < 14.4_5
14.3 <= FreeBSD < 14.3_14

Details

VuXML ID 90fe1784-54b6-11f1-8d7a-bc241121aa0a
Discovery 2026-05-20
Entry 2026-05-21

Problem Description:

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).

Impact:

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.

References

CVE Name CVE-2026-39461
FreeBSD Advisory SA-26:22.libcasper