FreeBSD p_cansignal privileges management

Summaryinfo

A vulnerability classified as critical was found in FreeBSD. Affected is the function p_cansignal. Executing a manipulation can lead to privileges management. The identification of this vulnerability is CVE-2026-45256. The attack can only be executed locally. There is no exploit available. It is advisable to implement a patch to correct this issue.

Detailsinfo

A vulnerability was found in FreeBSD (version unknown). It has been declared as critical. This vulnerability affects the function p_cansignal. The manipulation with an unknown input leads to a privileges management vulnerability. The CWE definition for the vulnerability is CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. As an impact it is known to affect availability. CVE summarizes:

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).

The weakness was shared by Yuxiang Yang, Yizhou Zhao, Ao Wang, Xuewei Feng, Qi Li and And Ke Xu. The advisory is shared for download at security.freebsd.org. This vulnerability was named CVE-2026-45256 since 05/11/2026. The exploitation appears to be easy. The attack needs to be approached locally. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 06/26/2026). The MITRE ATT&CK project declares the attack technique as T1068.

Applying a patch is able to eliminate this problem.

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Productinfo

Type

• Operating System

Name

• FreeBSD

License

• open-source

Website

• Product: https://www.freebsd.org/

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