CVE-2020-26242

### Impact Denial-of-service (crash) during block processing ### Details Affected versions suffer from a vulnerability which can be exploited through the `MULMOD` operation, by specifying a modulo of `0`: `mulmod(a,b,0)`, causing a `panic` in the underlying library. The crash was in the `uint256` library, where a buffer [underflowed](https://github.com/holiman/uint256/blob/4ce82e695c10ddad57215bdbeafb68b8c5df2c30/uint256.go#L442). if `d == 0`, `dLen` remains `0` and https://github.com/holiman/uint256/blob/4ce82e695c10ddad57215bdbeafb68b8c5df2c30/uint256.go#L451 will try to access index `[-1]`. The `uint256` library was first merged in this [commit](https://github.com/ethereum/go-ethereum/commit/cf6674539c589f80031f3371a71c6a80addbe454), on 2020-06-08. Exploiting this vulnerabilty would cause all vulnerable nodes to drop off the network. The issue was brought to our attention through a [bug report](https://github.com/ethereum/go-ethereum/issues/21367), showing a `panic` occurring on sync from genesis on the Ropsten network. It was estimated that the least obvious way to fix this would be to merge the fix into `uint256`, make a new release of that library and then update the geth-dependency. - https://github.com/holiman/uint256/releases/tag/v1.1.1 was made the same day, - PR to address the issue: https://github.com/holiman/uint256/pull/80 - PR to update geth deps: https://github.com/ethereum/go-ethereum/pull/21368 ### Patches Upgrade to v1.9.18 or higher ### Workarounds Not at this time ### References https://blog.ethereum.org/2020/11/12/geth_security_release/ ### For more information If you have any questions or comments about this advisory: * Open an issue in [go-ethereum](https://github.com/ethereum/go-ethereum) * Email us at [[email protected]](mailto:[email protected])