CVE-2026-45256 Missing permission check in thr_kill2(2)
An unprivileged local user can bypass permission checks to send signals to arbitrary processes, causing denial of service or privilege escalation.
- 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-2026-45256?
CVE-2026-45256 is a medium-severity missing authorization vulnerability in Freebsd Freebsd, published on 26 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
When used to deliver a signal to a specific thread, thr_kill2(2) called p_cansignal() to determine whether the operation was permitted but did not check the result before delivering the signal. The signal was sent even when the permission check failed. The system call returned the resulting error to the caller, but by then the signal had already been delivered.
The missing check allows an unprivileged local user who knows or can guess a target's process and thread IDs to send any signal to a process they would not normally be permitted to signal, including processes owned by other users or by root. The same check enforces jail boundaries, so a jailed process can signal processes on the host or in other jails. Thread IDs are allocated globally and sequentially, and so can be discovered by brute force with no visibility into the target.
An attacker can stop or terminate arbitrary processes, including critical system daemons, resulting in a Denial of Service (DoS).
Weakness: CWE-269
Which versions are affected by CVE-2026-45256?
It affects 1 product.
Products include Freebsd Freebsd.
How do I fix CVE-2026-45256?
No fix has been published for CVE-2026-45256 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-45256 being exploited?
There is no known exploitation of CVE-2026-45256 in the wild and no public exploit code.
Other vulnerabilities in Freebsd Freebsd
Sources
Also known as GHSA-hvc9-hvw8-q2fx.