In Eclipse Jetty, the Digest authentication server-side component uses ISO-8859-1 to encode the password as bytes.
This was done because the initial specification for HTTP did not specify explicitly a charset, and it was assumed to be ISO-8859-1 for historical reasons.
If the password contains characters that cannot be represented in ISO-8859-1, they are silently replaced by ?. This happens with passwords that contain Chinese, Cyrillic or Greek characters, for example: αβ123 converts to ??123.
An attacker can send a request with a digest Authorization header crafted with a password made of only ? characters; the server would match any password of the same length that contains non-ISO-8859-1 characters.
Recent HTTP Digest RFC-7616 supports a charset parameters that defaults to UTF-8 that allows for correct encoding/decoding of passwords.
Weakness
The product does not properly handle when an input uses an alternate encoding that is valid for the control sphere to which the input is being sent.
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/120.html
- https://cwe.mitre.org/data/definitions/267.html
- https://cwe.mitre.org/data/definitions/3.html
- https://cwe.mitre.org/data/definitions/4.html
- https://cwe.mitre.org/data/definitions/52.html
- https://cwe.mitre.org/data/definitions/53.html
- https://cwe.mitre.org/data/definitions/64.html
- https://cwe.mitre.org/data/definitions/71.html
- https://cwe.mitre.org/data/definitions/72.html
- https://cwe.mitre.org/data/definitions/78.html
- https://cwe.mitre.org/data/definitions/79.html
- https://cwe.mitre.org/data/definitions/80.html