CVE-2026-45251: freebsd Use-After-Free — Fix

Description

A file descriptor can be closed while a thread is blocked in a poll(2) or select(2) call waiting for that descriptor. Because the blocked thread does not hold a reference to the underlying object, this closure may result in the object being freed while the thread remains blocked. In this situation, the kernel must remove the blocked thread from the per-object wait queue prior to freeing the object. In the case of some file descriptor types, the kernel failed to unlink blocked threads from the object before freeing it. When the blocked thread is subsequently woken, it accesses memory that has already been freed resulting in a use-after-free vulnerability. The use-after-free vulnerability may be triggered by an unprivileged local user and can be exploited to obtain superuser privileges.

Is your site exposed to CVE-2026-45251?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0014

Probability of exploitation

0.04%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-416 Use After Free

Affected Products

Vendor	Product	Versions
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All
freebsd	freebsd	All

References

Advisories & Patches

https://security.freebsd.org/advisories/FreeBSD-SA-26:19.file.asc

Frequently Asked Questions

What is CVE-2026-45251? +

A file descriptor can be closed while a thread is blocked in a poll(2) or select(2) call waiting for that descriptor. Because the blocked thread does not hold a reference to the underlying object, this closure may result in the object being freed while the thread remains blocked. In this situation, the kernel must remove the blocked thread from the per-object wait queue prior to freeing the object. In the case of some file descriptor types, the kernel failed to unlink blocked threads from the object before freeing it. When the blocked thread is subsequently woken, it accesses memory that has already been freed resulting in a use-after-free vulnerability. The use-after-free vulnerability may be triggered by an unprivileged local user and can be exploited to obtain superuser privileges. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2026-45251? +

CVE-2026-45251 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0014, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-45251? +

CVE-2026-45251 affects products from freebsd, specifically: freebsd. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-45251? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-55406

Buffa is a pure-Rust Protocol Buffers implementation with first-class protobuf editions support. Prior to 0.7.0, a soundness bug in the …

CVE-2026-6040

A heap use-after-free existed when importing the blank-width characters of an ODF number format. A position value read from the …

CVE-2025-24898

rust-openssl is a set of OpenSSL bindings for the Rust programming language. In affected versions `ssl::select_next_proto` can return a slice …

CVE-2025-31115

XZ Utils provide a general-purpose data-compression library plus command-line tools. In XZ Utils 5.3.3alpha to 5.8.0, the multithreaded .xz decoder …

CVE-2025-31498

c-ares is an asynchronous resolver library. From 1.32.3 through 1.34.4, there is a use-after-free in read_answers() when process_answer() may re-enqueue …

CVE-2025-4516

There is an issue in CPython when using `bytes.decode("unicode_escape", error="ignore|replace")`. If you are not using the "unicode_escape" encoding or an …

CVE-2026-45251