When xdg-mail is configured to use thunderbird for mailto URLs, improper parsing of the URL can lead to additional headers being passed to thunderbird that should not be included per RFC 2368. An attacker can use this method to create a mailto URL that looks safe to users, but will actually attach files when clicked.
Weakness
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as expression or command delimiters when they are sent to a downstream component.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Xdg-utils |
Freedesktop |
1.1.0 (including) |
1.1.3 (including) |
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.
References