EUVD-2026-39963Severity by source
AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
Local-only attack requiring existing sandbox presence (AV:L, PR:L); scope changes because impact extends to external processes (S:C); only availability impacted via SIGKILL/SIGSTOP (A:H, C:N, I:N).
Primary rating from Vendor (freebsd).
CVSS VectorVendor: freebsd
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
Lifecycle Timeline
3DescriptionCVE.org
sigqueue(2) was marked as permitted in capability mode with the introduction of Capsicum in 2011, but the implementation of kern_sigqueue did not include a capability mode check restricting signal delivery to the calling process's own PID.
A process in capability mode can use sigqueue(2) to send signals to any process it could signal following standard Unix permissions, bypassing the Capsicum sandbox restriction. A compromised sandboxed process could interfere with other processes, for example by sending SIGKILL or SIGSTOP. This could be any process running as the same user, or any process, for a superuser sandboxed process.
AnalysisAI
Capsicum sandbox escape in FreeBSD allows a compromised capability-mode process to send arbitrary signals - including SIGKILL and SIGSTOP - to processes outside its sandbox, undermining Capsicum's core isolation guarantee. Affected are FreeBSD 14.3-RELEASE through 15.0-RELEASE in versions prior to their respective patch levels; the root cause is a 2011-era omission in kern_sigqueue that never enforced a PID self-restriction when a process operates in capability mode. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the attacker already control code executing inside a Capsicum capability-mode sandbox - specifically, a process that has called cap_enter(2) or been placed into capability mode by a parent process. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | CVSS 6.5 with S:C reflects a genuine sandbox escape with high availability impact, but several signals substantially dampen the urgency. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who has achieved code execution within a Capsicum-sandboxed application - for example, through a memory corruption bug in a sandboxed media parser or network service - invokes sigqueue(2) targeting the PID of a critical daemon (such as a logging service or authentication process) running under the same UID, sending SIGKILL to terminate it and cause a denial-of-service condition. No public exploit code has been identified at time of analysis, and the attack is non-automatable per SSVC, meaning exploitation requires deliberate, targeted effort following an initial compromise. |
| Remediation | Apply the vendor-released patches by upgrading to FreeBSD 15.0-RELEASE-p10, FreeBSD 14.4-RELEASE-p6, or FreeBSD 14.3-RELEASE-p15 as specified in FreeBSD-SA-26:28.capsicum.asc (https://security.freebsd.org/advisories/FreeBSD-SA-26:28.capsicum.asc). … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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