CVE-2026-102823

Russh is a Rust SSH client and server library. Prior to 0.63.1, a connection configured to permit mac=none can negotiate it with a MAC-requiring CTR or CBC block cipher because the selection logic validates needs_mac() only when MAC selection fails. A remote peer can then send a packet with a decrypted length of zero, causing russh/src/cipher/mod.rs to shrink the previously read block before indexing buffer.buffer[16..], which panics and terminates the connection task.

In russh, the agent server's Connection::try_sign path recognizes SSH_AGENT_CONSTRAIN_CONFIRM but returns a hard-coded success instead of calling Agent::confirm. A process that can reach the agent socket, including the remote side of a forwarded agent, can use a key added via ssh-add -c without the required approval and authenticate or sign data as the user. This is fixed in 0.65.0.

In the russh Rust SSH library from 0.60.0 until 0.65.0, channel-open parsing accepts a peer-declared maximum_packet_size of zero and passes it into ChannelTx::poll_writable. Asynchronous write paths remain pending forever, allowing an authenticated client to strand server writes and a malicious server to strand client writes.

In russh prior to 0.65.0, the client Session::process_packet path accepts repeated packets encoded with russh's private msg::EXT_INFO = 7 before authentication. The handle_ext_info function appends every parsed extension name to received_extensions without clearing, deduplicating, or bounding the vector, causing progressive client memory exhaustion.

russh before 0.65.0 in russh::keys::agent::server::serve accepts repeated SSH_AGENT_CONSTRAIN_CONFIRM records while adding a key and appends every Constraint::Confirm record to the key's retained constraint vector without a count or memory limit. A process that can connect to the agent socket, including the remote side of a forwarded agent session, can repeatedly add constrained keys and cause renewable memory growth that persists for the process lifetime because keys without a lifetime constraint do not expire. This is fixed in version 0.65.0.

In russh before 0.64.1, the agent server spawns a separate long-lived task for every SSH_AGENT_CONSTRAIN_LIFETIME record in a constrained add-key request. The loop accepts repeated records, clones the key blob into each task, and does not roll back tasks when later constraint parsing fails, allowing an attacker to exhaust memory and tasks.

Russh is a Rust SSH client and server library. Prior to 0.62.6, the USERAUTH_REQUEST path reached from server::run_stream in russh/src/server/encrypted.rs increments self.common.auth_attempts but never compares it with server::Config.max_auth_attempts. An unauthenticated remote client can continue submitting authentication requests on one connection beyond the configured cap, bypassing the deployment's attempt-limiting policy and increasing online guessing opportunity and backend authentication workload.

Russh is a Rust SSH client and server library. Prior to 0.63.0, the hybrid ML-KEM 768 and X25519 implementation in russh/src/kex/hybrid_mlkem.rs accepts an all-zero 32-byte peer X25519 public key in both server_dh and compute_shared_secret, forcing the X25519 contribution to the combined shared secret to zero. A malicious SSH peer can therefore make the combined secret depend only on ML-KEM, defeating the hybrid exchange's intended fallback protection if ML-KEM is later weakened. This issue is fixed in version 0.63.0.

Russh is a Rust SSH client and server library. Prior to 0.63.2, an authenticated remote peer can send SSH_MSG_KEXINIT without the required SSH_MSG_KEX_ECDH_INIT and then flood SSH_MSG_CHANNEL_OPEN messages while SessionKexState::InProgress prevents priority_receiver in russh/src/server/session.rs from being drained. The server continues processing network input and enqueues a ChannelOpenReply for each request on an unbounded channel, allowing one connection to grow memory until the process is terminated. This issue is fixed in version 0.63.2.

Russh prior to version 0.62.4 has a denial-of-service vulnerability. An authenticated SSH client can send a pty-req channel request with more than 130 terminal-mode records. The parser in russh/src/server/encrypted.rs stores terminal modes in a fixed 130-entry array but continues increasing the mode count, leading to an out-of-bounds slice and panic before the pty_request handler runs.