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Shallow copy bug in geth

Moderate severity GitHub Reviewed Published Nov 24, 2020 in ethereum/go-ethereum • Updated Jan 30, 2025

Package

gomod github.com/ethereum/go-ethereum (Go)

Affected versions

>= 1.9.7, < 1.9.17

Patched versions

1.9.17

Description

Impact

This is a Consensus vulnerability, 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,
  • calls 0x00..04 with R as an argument,
  • 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.

Patches

No standalone patches have been made.

Workarounds

Upgrade to 1.9.17 or higher.

References

https://blog.ethereum.org/2020/11/12/geth_security_release/

For more information

If you have any questions or comments about this advisory:

References

@holiman holiman published to ethereum/go-ethereum Nov 24, 2020
Reviewed May 21, 2021
Published to the GitHub Advisory Database Jun 29, 2021
Last updated Jan 30, 2025

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(36th percentile)

Weaknesses

CVE ID

CVE-2020-26241

GHSA ID

GHSA-69v6-xc2j-r2jf

Source code

Credits

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