CVE-2020-26241

Name of the Vulnerable Software and Affected Versions Geth versions prior to 1.9.17

Description This is a Consensus vulnerability in Geth that can be used to cause a chain-split where vulnerable nodes reject the canonical chain. Geth's pre-compiled dataCopy contract did a shallow copy on invocation. An attacker could deploy a contract that writes X to an EVM memory region R, then calls 0x00..04 with R as an argument, then overwrites R to Y, and finally invokes the RETURNDATACOPY opcode. When this contract is invoked, a consensus-compliant node would push X on the EVM stack, whereas Geth would push Y.

Recommendations Upgrade to version 1.9.17 or higher to resolve the issue. As a temporary workaround, consider restricting the use of the dataCopy contract until a patch is applied. Avoid using the RETURNDATACOPY opcode in conjunction with the dataCopy contract to minimize the risk of exploitation.