CVE-2026-39461 select(2) file descriptor set overflow causes stack overflow
A stack overflow in libcasper(3) allows local attackers to escalate privileges to root by triggering file descriptor set overflow.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-39461?
CVE-2026-39461 is a high-severity memory corruption vulnerability in Freebsd Freebsd, published on 21 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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).
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.
Weakness: CWE-121
Which versions are affected by CVE-2026-39461?
It affects 1 product.
Products include Freebsd Freebsd.
How do I fix CVE-2026-39461?
No fix has been published for CVE-2026-39461 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-39461 being exploited?
There is no known exploitation of CVE-2026-39461 in the wild and no public exploit code.
Other vulnerabilities in Freebsd Freebsd
Sources
Also known as GHSA-pwph-948j-pgvj.