All evidence, reproduction steps, and scripts in the report were verified against a real running instance. Nothing is fabricated or synthetic; every verdict is backed by captured output from an actual deployment. Concretely, the evidence comes from executing the real russh v0.64.1 client packet parser (Session::process_packet handling handle_ext_info) in a live client session with attacker-supplied packet bodies in the pre-authentication state; the captured output below is from that real execution. …
All evidence, reproduction steps, and scripts in the report were verified against a real running instance. Nothing is fabricated or synthetic; every verdict is backed by captured output from an actual deployment. The SSH agent server that ships with russh (russh::keys::agent::server::serve) parses client key-addition requests and, for each SSH_AGENT_CONSTRAIN_CONFIRM (0x02) record it finds, pushes one Constraint::Confirm value into a per-key vector inside an unbounded loop, then stores the resulting pair …
A peer can advertise maximum packet size = 0 in its channel-open message (CHANNEL_OPEN when attacking a server, CHANNEL_OPEN_CONFIRMATION when attacking a client). russh accepts the value without validation and copies it into the channel write state, where it caps the size of every outgoing data chunk. In the AsyncWrite code path (ChannelTx::poll_writable, used by Channel::data(), Channel::make_writer() and Channel::into_stream()), a cap of 0 makes every write future stay Poll::Pending forever: …
The agent server in russh::keys::agent::server never calls Agent::confirm before signing with a key that was added with the confirm constraint. That constraint is SSH_AGENT_CONSTRAIN_CONFIRM (RFC 9987 §5.2.7.2), which is what ssh-add -c sends. The call was replaced by a hard-coded true in 3e04597 ("Native async traits encore", #455), first released in 0.50.0-beta.12. Every release since, up to and including 0.64.1, signs requests for confirm-constrained keys without asking the Agent implementation. …
russh_keys::agent::server::add_key (russh/src/keys/agent/server.rs:271-319) spawns a dedicated tokio task for every 5-byte SSH_AGENT_CONSTRAIN_LIFETIME record attached to an added key, each cloning the key blob and sleeping for the declared lifetime (up to ~136 years). The loop has no per-request task budget, and spawned tasks are not rolled back when the overall request fails. Repeating one constrained add-key message over an agent connection converts wire bytes into resident tasks and heap at roughly …
This is a missing check on the signature algorithm (improper verification of a cryptographic signature's algorithm, CWE-347) in the server's publickey authentication. Who is impacted: applications that use russh as an SSH server and rely on the requested algorithm to restrict, record or audit user-key signature algorithms. For example: a server that refuses SHA-1 (ssh-rsa) signatures, as OpenSSH does by default since 8.8; a server that logs which algorithm a …
A russh server can be driven to unbounded heap growth (process OOM / kill) by a peer that speaks only standard SSH messages, in the default configuration. The peer starts a key re-exchange (sends SSH_MSG_KEXINIT) but never sends the follow-up SSH_MSG_KEX_ECDH_INIT, leaving the server's kex state machine in SessionKexState::InProgress indefinitely. While a rekey is in progress the server's three message-drain paths are all gated off (if !self.kex.active()), but the network-read …
SshBlockCipher implementations (AES-CBC, AES-CTR, 3DES-CBC, etc.) report needs_mac() == true, meaning they are documented/intended to always be paired with a separate integrity MAC. However, key-exchange negotiation only checks needs_mac() inside the fallback branch of MAC algorithm selection (used when no common MAC algorithm exists). If both peers' preferred MAC lists simply contain none and it is successfully negotiated through the normal selection path, nothing rejects pairing none with a cipher …
The purpose of hybrid key exchange is defense-in-depth: if either the classical algorithm (X25519) or the post-quantum algorithm (ML-KEM 768) is broken, the combined secret remains secure. By injecting a zero X25519 public key, an attacker eliminates the classical contribution entirely, reducing security to depend solely on ML-KEM. This matters in two scenarios: If ML-KEM 768 is later found to have a weakness (the explicit threat model hybrid KEX is …
Russh: Configured server auth-attempt cap is not enforced in the USERAUTH_REQUEST runtime path
CVE-2026-68930 was fixed by adding Session::is_established_channel() in russh/src/server/encrypted.rs, which gates every channel-scoped SERVER-side message (CHANNEL_REQUEST, CHANNEL_DATA, CHANNEL_EOF, CHANNEL_CLOSE, CHANNEL_WINDOW_ADJUST, CHANNEL_EXTENDED_DATA) on enc.channels.get(&channel).is_some_and(|c| c.confirmed) before invoking any Handler callback. The identical validation was never added to the CLIENT side (russh/src/client/encrypted.rs), which processes channel-scoped messages sent by the SSH SERVER once the client has authenticated.
There is a server-side channel state issue in russh. After a client is authenticated, russh can dispatch channel-scoped handler callbacks for recipient channel IDs that were never opened or confirmed. In the strongest reproduced case, the client does not send SSH_MSG_CHANNEL_OPEN at all. It authenticates normally, then sends SSH_MSG_CHANNEL_REQUEST packets with request type exec for a range of recipient channel IDs. russh still calls the server application's exec_request handler. This …
A pre-authentication denial-of-service panic in russh 0.62.2 (commit c4be19f1915c8682f4615c3fd50008512b474491, current default branch main as of 2026-07-22). An unauthenticated client sends a single SSH_MSG_KEX_ECDH_INIT whose Q_C is 32 zero bytes. russh's Curve25519 KEX does not reject the all-zero peer public value, so server_dh() computes the all-zero shared secret and compute_exchange_hash() then calls encode_mpint(&shared.0, …), which indexes s[i] at i == s.len() and panics (index out of bounds: the len is 32 …
A post-authentication denial-of-service panic in russh 0.62.2 (commit c4be19f1915c8682f4615c3fd50008512b474491, current default branch main as of 2026-07-22). An authenticated client sends a pty-req channel request carrying more than 130 terminal-mode records. The parser uses a fixed [(Pty::TTY_OP_END, 0); 130] array but increments its counter i for every valid record (logging "too many pty codes" without returning), then slices &modes[0..i] — an out-of-bounds slice that panics (range end index 131 out of …
A malicious SSH server can crash a russh client session with a single malformed key-exchange reply, causing a pre-authentication Denial-of-Service before the server host key is verified. The embedding process itself stays up, but the connection is killed deterministically.
In the russh client keyboard-interactive authentication path, a malicious SSH server could send a USERAUTH_INFO_REQUEST with an attacker-controlled prompt count, and the client would use that raw count directly in Vec::with_capacity(…) before validating that enough prompt data was actually present in the packet. This is a client-side denial-of-service / resource-exhaustion issue on the keyboard-interactive auth path.
russh did not enforce the SSH identification-string rules as deliberately as OpenSSH. In particular, the server-side identification reader used the same permissive path as the client, allowing pre-banner lines from clients, and the reader did not enforce a bounded number of pre-banner lines. For a library server built on russh, this could allow a remote peer to hold connection setup resources in the cleartext pre-authentication phase with malformed identification input …
Several russh client and server message handlers decoded attacker-controlled SSH strings, name-lists, and byte fields into owned allocations before applying field-specific bounds. A remote SSH peer could send oversized, high-fanout, or malformed length-prefixed fields and make the library allocate, attempt to allocate, or split data before rejecting input that should have been rejected earlier.
When SSH compression is enabled, russh accepted compressed packets whose on-wire size passed the normal transport packet-length checks but whose decompressed size was much larger. This allowed a remote peer to send oversized post-decompression packets that should have been rejected. In current releases, this is a remote denial-of-service / resource-exhaustion issue in the post-decompression receive path. In older releases before 0.58.0, the same remote decompression path used CryptoVec, which appears …
The russh server authentication path keeps internal userauth state across SSH_MSG_USERAUTH_REQUEST messages without separating that state when the request principal changes. RFC 4252 allows the user name and service name fields to change between authentication requests. The issue is not that such changes are invalid. The issue is that russh-owned authentication state, such as remaining methods, partial-success state, and in-progress method state, can remain associated with the connection and then …
CryptoVec used unchecked capacity growth, unchecked length arithmetic, and unsafe allocation/locking paths. In current russh releases, local SSH agent peers could still feed attacker-controlled frame lengths into buffer growth before validation. In older russh releases before 0.58.0, remote SSH traffic also reached CryptoVec through transport and compression buffers.
A pre-authentication denial-of-service vulnerability exists in the server's keyboard-interactive authentication handler. A malicious client can crash any russh-based server that implements keyboard-interactive auth (e.g., for 2FA/TOTP) with a single malformed packet, requiring no credentials.
A pre-authentication denial-of-service vulnerability exists in the server's keyboard-interactive authentication handler. A malicious client can crash any russh-based server that implements keyboard-interactive auth (e.g., for 2FA/TOTP) with a single malformed packet, requiring no credentials.