FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

FreeBSD -- Prefix Truncation Attack in the SSH protocol

Affected packages
14.0 <= FreeBSD < 14.0_4
13.2 <= FreeBSD < 13.2_9


VuXML ID 13d83980-9f18-11ee-8e38-002590c1f29c
Discovery 2023-12-19
Entry 2024-01-02

Problem Description:

The SSH protocol executes an initial handshake between the server and the client. This protocol handshake includes the possibility of several extensions allowing different options to be selected. Validation of the packets in the handshake is done through sequence numbers.


A man in the middle attacker can silently manipulate handshake messages to truncate extension negotiation messages potentially leading to less secure client authentication algorithms or deactivating keystroke timing attack countermeasures.


CVE Name CVE-2023-48795
FreeBSD Advisory SA-23:19.openssh