A flaw was found in libssh automatic certificate-based public key authentication. In sshuserauthpublickeyauto() in src/auth.c, the iterator over certificate candidates was not advanced correctly when configured certificates were missing or repeatedly rejected by the server. Under specific non-default certificate configurations, this could cause the client to restart the same authentication attempts indefinitely, leading to denial of service.

A flaw was found in libssh in the server-side GSSAPI Curve25519 key exchange path in src/kex-gss.c. In sshservergsskexprocessinit(), a client-controlled SSH string is unpacked into clientpubkey and then copied with memcpy(..., CURVE25519PUBKEYSIZE) without validating sshstringlen(clientpubkey). A remote unauthenticated client can send a short public key in SSHMSGKEXGSSINIT and trigger an out-of-bounds heap read during handshake processing, disclosing small amounts of adjacent server memory.

A flaw was found in libssh server-side SFTP directory listing. In processreaddir() in src/sftpserver.c, the server allocates a fixed stack buffer as char longname[MAXLONGNAMELEN] and passes attacker-controlled directory entry names into readdirlongname(). In the pre-patch implementation, readdirlongname() appends metadata and the filename into zlongname with repeated unbounded strcat() calls. Because zlongname points at the caller-owned fixed stack buffer, sufficiently long filenames in an attacker-controlled directory can overflow that stack buffer during SSHFXPREADDIR processing, leading to crashes and possible code execution on the server.