Crayfish is a collection of Islandora 8 microservices, one of which, Homarus, provides FFmpeg as a microservice. Prior to Crayfish version 4.1.0, remote code execution may be possible in web-accessible installations of Homarus in certain configurations. The issue has been patched in islandora/crayfish:4.1.0. Some workarounds are available. The exploit requires making a request against the Homaruss /convert endpoint; therefore, the ability to exploit is much reduced if the microservice is not directly accessible from the Internet, so: Prevent general access from the Internet from hitting Homarus. Alternatively or additionally, configure auth in Crayfish to be more strongly required, such that requests with Authorization headers that do not validate are rejected before the problematic CLI interpolation occurs.
Weakness
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as escape, meta, or control character sequences when they are sent to a downstream component.
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