OESA-2026-3321

The ssh library was designed to be used by programmers needing a working SSH implementation by the mean of a library. The complete control of the client is made by the programmer. With libssh, you can remotely execute programs, transfer files, use a secure and transparent tunnel for your remote programs. With its Secure FTP implementation, you can play with remote files easily, without third-party programs others than libcrypto (from openssl).

Security Fix(es):

A flaw was found in libssh. A remote authenticated peer can advertise a zero maximum packet size in SSHMSGCHANNEL_OPEN, causing later channel writes to loop indefinitely and consume CPU, leading to denial of service.(CVE-2026-59843)

A flaw was found in libssh. A remote authenticated client can issue SSHFXPREAD requests with an arbitrarily large length, causing a libssh SFTP server to allocate excessive memory and potentially exhaust it through repeated requests.(CVE-2026-59844)

A flaw was found in libssh. When ProxyCommand is used, an unchecked fork() failure can be stored as process ID -1; during cleanup, signals may then be sent across the caller's accessible process tree, leading to local denial of service.(CVE-2026-59845)

A flaw was found in libssh. Incorrect AES-GCM finalization checks in builds using the OpenSSL backend can effectively remove integrity protection, allowing an in-path attacker to modify plaintext on the wire without detection.(CVE-2026-59847)

A flaw was found in libssh. If data packets are processed after a channel is closed, channel data callbacks can be invoked after the associated data has already been freed, leading to crashes or possible use-after-free conditions.(CVE-2026-59850)