FreeBSDOperating system
CVE-2026-45256
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedWhen 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).
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA race condition/_logic error in FreeBSD's thr_kill2(2) system call allows unprivileged local users to send arbitrary signals to any process by exploiting a missing return-value check on p_cansignal(). The permission check is performed but its result is ignored, so signals are delivered regardless of authorization. Thread IDs can be brute-forced due to global sequential allocation.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
FreeBSDOperating system
= 14.3= 14.4= 15.0= 15.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check FreeBSD versionRun `freebsd-version` or `uname -a` to determine the installed FreeBSD versionAffected if The version matches 14.3, 14.4, 15.0, or 15.1
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Verify kernel patch statusCheck for the presence of the fix in the kernel source or installed patches. If the system has been updated post-CVE disclosure, the fix may be present in a newer errata or security advisory update.Affected if The kernel is at an affected version AND has not been updated with the vendor patch that adds proper p_cansignal() return-value checking before signal delivery in thr_kill2(2)
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Test thr_kill2 system call behaviorAs a non-root user, attempt to use the thr_kill2(2) system call to send a signal to a privileged process running as a different user. If signal delivery succeeds despite lacking authorization, the system is vulnerable.Affected if Unprivileged users can successfully send signals to processes they do not own or have no permission to signal, confirming the missing p_cansignal() return-value check is exploitable
A system is affected if it runs FreeBSD 14.3, 14.4, 15.0, or 15.1 and the vendor patch for CVE-2026-45256 has not been applied, allowing any local unprivileged user to send arbitrary signals to any process.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply the vendor patch for FreeBSD that adds proper error checking before signal delivery in thr_kill2(2); consider kernel flags or mandatory access controls as temporary workarounds if available.
Fix this in FreeBSD
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing16.0 h
- Review / QA8.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $9,728.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-45256 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-45256 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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