Soft Serve is a self-hostable Git server for the command line. Versions 0.11.2 and below have a critical authentication bypass vulnerability that allows an attacker to impersonate any user (including admin) by offering the victims public key during the SSH handshake before authenticating with their own valid key. This occurs because the user identity is stored in the session context during the offer phase and is not cleared if that specific authentication attempt fails. This issue has been fixed in version 0.11.3.
Weakness
The product performs authentication based on the name of a resource being accessed, or the name of the actor performing the access, but it does not properly check all possible names for that resource or actor.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Soft_serve | Charm | * | 0.11.3 (excluding) |
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.