decode_error
decode_error (50) is sent when a TLS message cannot be decoded because a field is out of the specified range or the length of the message is incorrect. The data was received but cannot be parsed as a valid TLS structure. This is a protocol-layer parsing failure, not an application-level error.
Alert Code
50
Level
Fatal
Standard
RFC 8446
Description
decode_error fires when TLS record parsing fails – a field value does not match the expected format, a vector length exceeds bounds, or an enum value is not valid. For example, a ClientHello with a legacy_version field set to an unknown value, or a handshake message with a length that extends beyond the record boundary. This indicates either a buggy TLS implementation on the peer side or network corruption that modified the TLS handshake bytes.
Common Causes
- –Handshake message length field inconsistent with actual data
- –Enum field contains an unknown or invalid value
- –Extension data length exceeds the extension payload
- –Network corruption modifying handshake bytes
- –TLS implementation bug producing malformed messages