CVE-2021-39193

Frontier is Substrates Ethereum compatibility layer. Prior to commit number 0b962f218f0cdd796dadfe26c3f09e68f7861b26, a bug in pallet-ethereum can cause invalid transactions to be included in the Ethereum block state in pallet-ethereum due to not validating the input data size. Any invalid transactions included this way have no possibility to alter the internal Ethereum or Substrate state. The transaction will appear to have be included, but is of no effect as it is rejected by the EVM engine. The impact is further limited by Substrate extrinsic size constraints. A patch is available in commit number 0b962f218f0cdd796dadfe26c3f09e68f7861b26. There are no workarounds aside from applying the patch.

Weakness

The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.

Affected Software

Extended Description

Specified quantities include size, length, frequency, price, rate, number of operations, time, and others. Code may rely on specified quantities to allocate resources, perform calculations, control iteration, etc. When the quantity is not properly validated, then attackers can specify malicious quantities to cause excessive resource allocation, trigger unexpected failures, enable buffer overflows, etc.

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

• https://github.com/paritytech/frontier/commit/0b962f218f0cdd796dadfe26c3f09e68f7861b26
• https://github.com/paritytech/frontier/pull/465
• https://github.com/paritytech/frontier/pull/465/commits/8a2b890a2fb477d5fedd0e4335b00623832849ae
• https://github.com/paritytech/frontier/security/advisories/GHSA-hw4v-5x4h-c3xm