Summary
Erroneous Proof of Work calculation in geth
Workarounds
This PR implements a patch: https://github.com/ethereum/go-ethereum/pull/21793
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 [email protected]
Impact
An ethash mining DAG generation flaw in Geth could cause miners to erroneously calculate PoW in an upcoming epoch (estimated early January, 2021). This happened on the ETC chain on 2020-11-06. This issue is relevant only for miners, non-mining nodes are unaffected.
CVE-2020-26240 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (1.9.24); 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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This issue is also fixed as of 1.9.24. Thanks to @slavikus for bringing the issue to our attention and writing the fix.
Frequently Asked Questions
- What is CVE-2020-26240? CVE-2020-26240 is a medium-severity security vulnerability in github.com/ethereum/go-ethereum (go), affecting versions < 1.9.24. It is fixed in 1.9.24.
- How severe is CVE-2020-26240? CVE-2020-26240 has a CVSS score of 5.3 (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-2020-26240? github.com/ethereum/go-ethereum (go) versions < 1.9.24 is affected.
- Is there a fix for CVE-2020-26240? Yes. CVE-2020-26240 is fixed in 1.9.24. Upgrade to this version or later.
- Is CVE-2020-26240 exploitable, and should I be worried? Whether CVE-2020-26240 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-2020-26240 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-2020-26240? Upgrade
github.com/ethereum/go-ethereumto 1.9.24 or later.