{"record":{"id":"419685fb6330d1e9","repo":"jstedfast/MailKit","slug":"incompletechallenge-challenge-did-not-contain-a-salt","errorCode":"IncompleteChallenge","errorMessage":"Challenge did not contain a salt.","messagePattern":"Challenge did not contain a salt\\.","errorType":"error_code","errorClass":"SaslException","httpStatus":null,"severity":"error","filePath":"MailKit/Security/SaslMechanismScramBase.cs","lineNumber":345,"sourceCode":"\t\t\t\t\t\tchannelBindingKind = ChannelBindingKind.Unknown;\n\t\t\t\t\t}\n\t\t\t\t}\n\n\t\t\t\tinput = GetChannelBindingInput (channelBindingKind, AuthorizationId);\n\t\t\t\tresponse = Encoding.UTF8.GetBytes (input + client);\n\t\t\t\tstate = LoginState.Final;\n\t\t\t\tbreak;\n\t\t\tcase LoginState.Final:\n\t\t\t\tif (token == null)\n\t\t\t\t\tthrow new SaslException (MechanismName, SaslErrorCode.MissingChallenge, \"Server response did not contain any authentication data.\");\n\n\t\t\t\tserver = Encoding.UTF8.GetString (token, startIndex, length);\n\t\t\t\tvar tokens = ParseServerChallenge (server);\n\t\t\t\tstring? salt, nonce, iterations;\n\t\t\t\tint count;\n\n\t\t\t\tif (!tokens.TryGetValue ('s', out salt))\n\t\t\t\t\tthrow new SaslException (MechanismName, SaslErrorCode.IncompleteChallenge, \"Challenge did not contain a salt.\");\n\n\t\t\t\tif (!tokens.TryGetValue ('r', out nonce))\n\t\t\t\t\tthrow new SaslException (MechanismName, SaslErrorCode.IncompleteChallenge, \"Challenge did not contain a nonce.\");\n\n\t\t\t\tif (!tokens.TryGetValue ('i', out iterations))\n\t\t\t\t\tthrow new SaslException (MechanismName, SaslErrorCode.IncompleteChallenge, \"Challenge did not contain an iteration count.\");\n\n\t\t\t\tif (!nonce.StartsWith (cnonce!, StringComparison.Ordinal))\n\t\t\t\t\tthrow new SaslException (MechanismName, SaslErrorCode.InvalidChallenge, \"Challenge contained an invalid nonce.\");\n\n\t\t\t\tif (!int.TryParse (iterations, NumberStyles.None, CultureInfo.InvariantCulture, out count) || count < 1)\n\t\t\t\t\tthrow new SaslException (MechanismName, SaslErrorCode.InvalidChallenge, \"Challenge contained an invalid iteration count.\");\n\n\t\t\t\tvar password = Encoding.UTF8.GetBytes (SaslPrep (Credentials.Password));\n\t\t\t\tsalted = Hi (password, Convert.FromBase64String (salt), count);\n\t\t\t\tArray.Clear (password, 0, password.Length);\n\n\t\t\t\tinput = GetChannelBindingInput (channelBindingKind, AuthorizationId);","sourceCodeStart":327,"sourceCodeEnd":363,"githubUrl":"https://github.com/jstedfast/MailKit/blob/9d3859a7855e3e17582c07fd01972b8e262bf176/MailKit/Security/SaslMechanismScramBase.cs#L327-L363","documentation":"When parsing the SCRAM server-first message, MailKit requires the 's' (salt, base64) attribute per RFC 5802. If the parsed challenge tokens contain no 's' entry, SaslException with SaslErrorCode.IncompleteChallenge is thrown. Without the salt the client cannot compute the salted password (Hi function) and cannot proceed.","triggerScenarios":"Calling Challenge() on a SCRAM mechanism when the server-first message (e.g. \"r=...,i=4096\") is missing the s=<base64-salt> attribute.","commonSituations":"Non-conformant SCRAM server implementations, servers omitting the salt due to a bug or misconfigured user database entry (no stored salt for that user).","solutions":["Log the raw server-first message and confirm which SCRAM attributes it contains","Check the server's authentication database — the user's stored SCRAM salt may be missing/corrupt; re-provision the user","Use a different mechanism (PLAIN over TLS) if the server's SCRAM implementation is incomplete","Catch SaslException with ErrorCode == SaslErrorCode.IncompleteChallenge and fall back to another mechanism"],"exampleFix":"// before\nclient.Authenticate (new SaslMechanismScramSha1 (\"user\", \"pass\")); // server omits s=\n// after\ntry {\n    client.Authenticate (new SaslMechanismScramSha1 (\"user\", \"pass\"));\n} catch (SaslException ex) when (ex.ErrorCode == SaslErrorCode.IncompleteChallenge) {\n    client.Authenticate (new SaslMechanismPlain (\"user\", \"pass\"));\n}","handlingStrategy":"try-catch","validationCode":"// Cannot inspect the server-first message pre-auth; guard at the mechanism level:\nif (!client.AuthenticationMechanisms.Any (m => m.StartsWith (\"SCRAM-\")))\n    usePlainOverTls = true;","typeGuard":null,"tryCatchPattern":"try {\n    client.Authenticate (scramMechanism);\n} catch (SaslException ex) when (ex.ErrorCode == SaslErrorCode.IncompleteChallenge) {\n    // server-first message missing salt/nonce/iterations; use another mechanism\n}","preventionTips":["Fix server-side user records so SCRAM salt/iterations always exist","Fall back to PLAIN over TLS when SCRAM is unreliable","Capture raw challenges with an IProtocolLogger when diagnosing","Prefer servers with conformance-tested SCRAM implementations"],"tags":["sasl","scram","authentication","mailkit"],"backgroundTag":"unexpected-response-shape","analyzedSha":"9d3859a7855e3e17582c07fd01972b8e262bf176","analyzedAt":"2026-09-15T15:46:11.592Z","contentChangedAt":"2026-09-15T15:46:11.592Z","schemaVersion":2},"datasetVersion":"2026-09-15T23:17:13.987Z"}