Denial of service in geth

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.

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, 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, 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
• Email us at security@ethereum.org