@hono/node-server allows running the Hono application on Node.js. From 1.19.10 until 2.1.3, serveStatic decodes a request path a second time after Hono has already decoded it for routing, so a malformed percent-encoded sequence can make route middleware evaluate an encoded path while static file resolution uses a different directory. An unauthenticated attacker can bypass middleware mounted on a protected static prefix and read a file inside the configured static root, although the flaw does not permit traversal outside that root. This issue is fixed in version 2.1.3.
Weakness
The product decodes the same input twice, which can limit the effectiveness of any protection mechanism that occurs in between the decoding operations.
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.