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OpenZeppelin Contracts base64 encoding may read from potentially dirty memory

Moderate severity GitHub Reviewed Published Feb 29, 2024 in OpenZeppelin/openzeppelin-contracts • Updated Dec 4, 2025

Package

npm @openzeppelin/contracts (npm)

Affected versions

>= 4.5.0, < 4.9.6
>= 5.0.0-rc.0, < 5.0.2

Patched versions

4.9.6
5.0.2
npm @openzeppelin/contracts-upgradeable (npm)
>= 5.0.0-rc.0, < 5.0.2
>= 4.5.0, < 4.9.6
5.0.2
4.9.6

Description

Impact

The Base64.encode function encodes a bytes input by iterating over it in chunks of 3 bytes. When this input is not a multiple of 3, the last iteration may read parts of the memory that are beyond the input buffer.

Although the encode function pads the output for these cases, up to 4 bits of data are kept between the encoding and padding, corrupting the output if these bits were dirty (i.e. memory after the input is not 0). These conditions are more frequent in the following scenarios:

  • A bytes memory struct is allocated just after the input and the first bytes of it are non-zero.
  • The memory pointer is set to a non-empty memory location before allocating the input.

Developers should evaluate whether the extra bits can be maliciously manipulated by an attacker.

Patches

Upgrade to 5.0.2 or 4.9.6.

References

This issue was reported by the Independent Security Researcher Riley Holterhus through Immunefi (@rileyholterhus on X)

References

@ernestognw ernestognw published to OpenZeppelin/openzeppelin-contracts Feb 29, 2024
Published to the GitHub Advisory Database Feb 29, 2024
Reviewed Feb 29, 2024
Published by the National Vulnerability Database Mar 21, 2024
Last updated Dec 4, 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
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High

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:H/PR:N/UI:N/S:U/C:N/I:L/A:H

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.
(67th percentile)

Weaknesses

Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer. Learn more on MITRE.

CVE ID

CVE-2024-27094

GHSA ID

GHSA-9vx6-7xxf-x967

Source code

Credits

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