CyberSecBulletin
CVE-2026-45257NVD status: Analyzed

FreeBSD: Write-what-where Condition

Published Updated By the CyberSecBulletin desk

CVE-2026-45257 is a high-severity write-what-where condition vulnerability in FreeBSD, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions p10, p6, p15 as the first without the flaw, so updating FreeBSD to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.18% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update FreeBSD to p10 or p6 or p15, whichever matches your release line, or a later version.
  2. Read the advisory on security.freebsd.org for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
FreeBSDFreeBSD15.0-RELEASE up to, but not including, p10; 14.4-RELEASE up to, but not including, p6; 14.3-RELEASE up to, but not including, p15p10, p6, p15

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).

Official description

The KTLS receive path decrypted each record in place, assuming that the mbufs holding received data were anonymous and safe to modify. This assumption does not hold for data placed on a socket by sendfile(2), which can reference file-backed memory directly through non-anonymous M_EXTPG pages or EXT_SFBUF mbufs. When the sender transmits such data over a loopback connection without enabling KTLS on the transmit side, the file-backed mbufs reach the receiver's decryption path unchanged. Decrypting a record in place then overwrites the backing file's page cache instead of a private copy of the data. An unprivileged local user who can read a file can overwrite its contents with data of their choosing by sending the file over a loopback connection on which they have enabled KTLS receive. The write modifies the page cache directly, so it bypasses file flags such as schg and is written back to disk. By overwriting a setuid binary or other trusted file, a local user can escalate privileges, potentially gaining full control of the affected system.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Write-what-where Condition

Any condition where the attacker has the ability to write an arbitrary value to an arbitrary location, often as the result of a buffer overflow.

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.
  • Use OS-level preventative functionality integrated after the fact. Not a complete solution.

More Write-what-where Condition vulnerabilities (CWE-123)

Timeline

  1. CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
  2. CVE record published.
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in FreeBSD

All FreeBSD vulnerabilities

Recent Write-what-where Condition vulnerabilities

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