FreeBSD write-what-where condition

Summaryinfo

A vulnerability, which was classified as critical, was found in FreeBSD. Affected by this issue is some unknown functionality. The manipulation results in write-what-where condition. This vulnerability is identified as CVE-2026-45257. The attack is only possible with local access. There is not any exploit available. It is best practice to apply a patch to resolve this issue.

Detailsinfo

A vulnerability classified as critical has been found in FreeBSD (affected version not known). Affected is some unknown functionality. The manipulation with an unknown input leads to a write-what-where condition vulnerability. CWE is classifying the issue as CWE-123. 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. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The weakness was released by Bumsrakete. The advisory is available at security.freebsd.org. This vulnerability is traded as CVE-2026-45257 since 05/11/2026. The exploitability is told to be easy. Local access is required to approach this attack. The technical details are unknown and an exploit is not available. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 06/26/2026).

Applying a patch is able to eliminate this problem.

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Productinfo

Type

• Operating System

Name

• FreeBSD

License

• open-source

Website

• Product: https://www.freebsd.org/

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