PatchSiren cyber security CVE debrief

CVE-2026-45259 FreeBSD CVE debrief

CVE-2026-45259 is a vulnerability in the FreeBSD operating system's Capsicum implementation. The sigqueue(2) system call was incorrectly permitted in capability mode, allowing a sandboxed process to send signals to other processes, potentially bypassing sandbox restrictions. A compromised sandboxed process could interfere with other processes by sending signals such as SIGKILL or SIGSTOP. This could affect any process running as the same user or any process for a superuser sandboxed process. The vulnerability has a CVSS score of 6.5 and a severity of MEDIUM.

Vendor: FreeBSD
Product: Unknown
CVSS: MEDIUM 6.5
CISA KEV: Not listed in stored evidence
Original CVE published: 2026-06-27
Original CVE updated: 2026-06-29
Advisory published: 2026-06-27
Advisory updated: 2026-06-29

Who should care

System administrators and security teams responsible for FreeBSD systems should be aware of this vulnerability. They should assess their system's exposure and apply patches or mitigations as necessary. Additionally, developers working with Capsicum or sandboxing in FreeBSD should review the implementation to prevent similar issues.

Technical summary

The vulnerability arises from the incorrect implementation of kern_sigqueue in the context of Capsicum's capability mode. When a process is in capability mode, it should have restricted capabilities, but due to this flaw, it can use sigqueue(2) to send signals to any process it could signal following standard Unix permissions. This bypasses the intended Capsicum sandbox restriction, allowing potentially malicious sandboxed processes to affect other processes on the system.

Defensive priority

Apply patches or updates provided by the vendor (FreeBSD) as soon as possible. Review and update system configurations to ensure that Capsicum is properly implemented and that sandboxed processes are correctly restricted.

Recommended defensive actions

Apply the official patch from FreeBSD to correct the Capsicum implementation.
Review system configurations to ensure proper sandboxing and restrictions.
Monitor system logs for suspicious activity related to sigqueue(2) and signal delivery.
Implement additional monitoring and logging to detect potential exploitation attempts.
Consider compensating controls, such as restricting process capabilities, until a patch is applied.

Evidence notes

The CVE and NVD provide official details on the vulnerability. The FreeBSD security advisory (FreeBSD-SA-26:28.capsicum.asc) offers specific information on the impact and mitigation. The vulnerability's CVSS score and severity are based on the CVSS:3.1 vector provided.

Official resources

This article is AI-assisted and based on the supplied source corpus.