Source-address critical option not enforced for non-public-key auth callbacks in golang.org/x/crypto/ssh
The source-address critical option in the Permissions returned by an authentication callback was only enforced for the PublicKeyCallback and VerifiedPublicKeyCallback paths, extending the fix for CVE-2026-46595. Permissions returned by the PasswordCallback, KeyboardInteractiveCallback, NoClientAuthCallback, and GSSAPIWithMICConfig.AllowLogin callbacks were not validated against the client's remote address, so a source-address restriction set by those callbacks was silently ignored. The check is now applied to the Permissions returned by any authentication callback.
Invoking auth bypass via unenforced @revoked status in golang.org/x/crypto/ssh/knownhosts
Previously, a revoked 'SignatureKey' belonging to a CA was not correctly checked for revocation. Now, both the 'key' and 'key.SignatureKey' are checked for @revoked.
Invoking infinite loop on large channel writes in golang.org/x/crypto/ssh
When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.
Invoking bypass of FIDO/U2F security keys physical interaction in golang.org/x/crypto/ssh
The Verify() method for FIDO/U2F security key types ([email protected], [email protected]) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.
Invoking pathological RSA/DSA parameters may cause DoS in golang.org/x/crypto/ssh
The RSA and DSA public key parsers did not enforce size limits on key parameters. A crafted public key with an excessively large modulus or DSA parameter could cause several minutes of CPU consumption during signature verification. This could be triggered by unauthenticated clients during public key authentication. RSA moduli are now limited to 8192 bits, and DSA parameters are validated per FIPS 186-2.
Invoking client can cause server deadlock on unexpected responses in golang.org/x/crypto/ssh
A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.
Invoking memory leak when rejecting channels can lead to DoS in golang.org/x/crypto/ssh
An authenticated SSH client that repeatedly opened channels which were rejected by the server caused unbounded memory growth, eventually crashing the server process and affecting all connected users. Rejected channels are now properly removed from the connection's internal state and released for garbage collection.
Invoking server panic during CheckHostKey/Authenticate in golang.org/x/crypto/ssh
SSH servers which use CertChecker as a public key callback without setting IsUserAuthority or IsHostAuthority could be caused to panic by a client presenting a certificate. CertChecker now returns an error instead of panicking when these callbacks are nil.
Invoking bypass of certificate restrictions in golang.org/x/crypto/ssh
When an SSH server authentication callback returned PartialSuccessError with non-nil Permissions, those permissions were silently discarded, potentially dropping certificate restrictions such as force-command after a second factor succeeded. Returning non-nil Permissions with PartialSuccessError now results in a connection error.
Invoking agent constraints dropped when forwarding keys in golang.org/x/crypto/ssh/agent
When adding a key to a remote agent constraint extensions such as [email protected] were not serialized in the request. Destination restrictions were silently stripped when forwarding keys, allowing unrestricted use of the key on the remote host. The client now serializes all constraint extensions. Additionally, the in-memory keyring returned by NewKeyring() now rejects keys with unsupported constraint extensions instead of silently ignoring them.
Invoking key constraints not enforced in golang.org/x/crypto/ssh/agent
The in-memory keyring returned by NewKeyring() silently accepted keys with the ConfirmBeforeUse constraint but never enforced it. The key would sign without any confirmation prompt, with no indication to the caller that the constraint was not in effect. NewKeyring() now returns an error when unsupported constraints are requested.
Malformed constraint may cause denial of service in golang.org/x/crypto/ssh/agent
SSH Agent servers do not validate the size of messages when processing new identity requests, which may cause the program to panic if the message is malformed due to an out of bounds read.
Unbounded memory consumption in golang.org/x/crypto/ssh
SSH servers parsing GSSAPI authentication requests do not validate the number of mechanisms specified in the request, allowing an attacker to cause unbounded memory consumption.
Potential denial of service in golang.org/x/crypto
SSH servers which implement file transfer protocols are vulnerable to a denial of service attack from clients which complete the key exchange slowly, or not at all, causing pending content to be read into memory, but never transmitted.
Usage of IPv6 zone IDs can bypass URI name constraints in crypto/x509
A certificate with a URI which has a IPv6 address with a zone ID may incorrectly satisfy a URI name constraint that applies to the certificate chain. Certificates containing URIs are not permitted in the web PKI, so this only affects users of private PKIs which make use of URIs.
Misuse of connection.serverAuthenticate may cause authorization bypass in golang.org/x/crypto
Applications and libraries which misuse connection.serverAuthenticate (via callback field ServerConfig.PublicKeyCallback) may be susceptible to an authorization bypass. The documentation for ServerConfig.PublicKeyCallback says that "A call to this function does not guarantee that the key offered is in fact used to authenticate." Specifically, the SSH protocol allows clients to inquire about whether a public key is acceptable before proving control of the corresponding private key. PublicKeyCallback may be called with multiple keys, and the order in which the keys were provided cannot be used to infer which key the client successfully authenti
The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remote attackers to bypass integrity checks such that some packets are omitted (from the extension negotiation message), and a client and server may consequently end up with a connection for which some security features have been downgraded or disabled, aka a Terrapin attack. This occurs because the SSH Binary Packet Protocol (BPP), implemented by these extensions, mishandles the handshake phase and mishandles use of sequence numbers. For example, there is an effective attack against SSH's use of ChaCha20-Poly1305 (and CBC with E