OpenZeppelin Contracts base64 encoding may read from potentially dirty memory
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 memorystruct 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)
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @openzeppelin/contracts | >= 4.5.0, < 4.9.6, >= 5.0.0-rc.0, < 5.0.2 | 4.9.6, 5.0.2 |
| npm package | @openzeppelin/contracts-upgradeable | >= 5.0.0-rc.0, < 5.0.2, >= 4.5.0, < 4.9.6 | 5.0.2, 4.9.6 |
References
- https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-9vx6-7xxf-x967
- https://nvd.nist.gov/vuln/detail/CVE-2024-27094
- https://github.com/OpenZeppelin/openzeppelin-contracts-upgradeable/commit/2d081f24cac1a867f6f73d512f2022e1fa987854
- https://github.com/OpenZeppelin/openzeppelin-contracts-upgradeable/commit/723f8cab09cdae1aca9ec9cc1cfa040c2d4b06c1
- https://github.com/OpenZeppelin/openzeppelin-contracts/commit/92224533b1263772b0774eec3134e132a3d7b2a6
- https://github.com/OpenZeppelin/openzeppelin-contracts/commit/a6286d0fded8771b3a645e5813e51993c490399c
- https://github.com/OpenZeppelin/openzeppelin-contracts
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H- Weakness (CWE)
CWE-125- Platform
- npm
- Package
@openzeppelin/contracts, @openzeppelin/contracts-upgradeable- Disclosed
- 29.02.2024
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9vx6-7xxf-x967 - CC BY 4.0
Vulnerability history: @openzeppelin/contracts
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 20
- First → latest
- 08.2021 07.2025
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 5
- Medium 12
- Low 1
Disclosures per year
- 2021: 4
- 2022: 7
- 2023: 7
- 2024: 1
- 2025: 1
- 2026: 0
-
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