Summary
Ethereum Contains Consensus Flaw During Block Processing
Description
A memory-corruption bug within the EVM can cause a consensus error, where vulnerable nodes obtain a different stateRoot when processing a maliciously crafted transaction. This, in turn, would lead to the chain being split in two forks.
All Geth versions supporting the London hard fork are vulnerable (which predates London), so all users should update.
This bug was exploited on Mainnet at block 13107518, leading to a minority chain split.
Workarounds
No workarounds exist, save to update and/or apply the patch commit.
References.
Post-mortem write-up.
Credits
The bug was found by @guidovranken (working for Sentnl during an audit of the Telos EVM) and reported via [email protected].
For more information
If you have any questions or comments about this advisory:
- Open an issue in go-ethereum
- Email us at [email protected]
Impact
A vulnerability in the Geth EVM could cause a node to reject the canonical chain.
CVE-2021-39137 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.10.8); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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A patch is included in the v1.10.8 release.
The exact patch to fix the issue is contained within this commit
Frequently Asked Questions
- What is CVE-2021-39137? CVE-2021-39137 is a medium-severity security vulnerability in github.com/ethereum/go-ethereum (go), affecting versions >= 1.10.0, < 1.10.8. It is fixed in 1.10.8.
- How severe is CVE-2021-39137? CVE-2021-39137 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/ethereum/go-ethereum are affected by CVE-2021-39137? github.com/ethereum/go-ethereum (go) versions >= 1.10.0, < 1.10.8 is affected.
- Is there a fix for CVE-2021-39137? Yes. CVE-2021-39137 is fixed in 1.10.8. Upgrade to this version or later.
- Is CVE-2021-39137 exploitable, and should I be worried? Whether CVE-2021-39137 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-39137 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-39137? Upgrade
github.com/ethereum/go-ethereumto 1.10.8 or later.