CVE-2024-27094 (Other, published 2024-03-21T02:52Z)
Description: value: OpenZeppelin Contracts is a library for secure smart contract development. 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. The vulnerability is fixed in 5.0.2 and 4.9.6.
Severity: nan (CVSS v3 base score: )
Weakness: NVD-CWE-noinfo \u2014 Insufficient Information
There is insufficient information about the issue to classify it; details are unkown or unspecified.
Repository: https://github.com/OpenZeppelin/openzeppelin-contracts
Files changed:
.changeset/warm-geese-dance.md
contracts/mocks/Base64Dirty.sol
contracts/utils/Base64.sol
test/utils/Base64.test.js
Commit message: Merge pull request from GHSA-9vx6-7xxf-x967

* add tests for the encode reads dirty data issue

* Fix the encode reads dirty data issue

* add changeset

* trigger the issue without assembly

* rename mock

* gas optimization

* Apply suggestions from code review

Co-authored-by: Ernesto García <ernestognw@gmail.com>

* alternative fix: cheaper

* update comment

* fix lint

---------

Co-authored-by: Ernesto García <ernestognw@gmail.com>

Vulnerable code:
            let resultPtr := add(result, 32)
                let dataPtr := data
                let endPtr := add(data, mload(data))
                // To write each character, shift the 3 bytes (18 bits) chunk
                // and apply logical AND with 0x3F which is the number of
                // the previous character in the ASCII table prior to the Base64 Table
                // The result is then added to the table to get the character to write,
                // and finally write it in the result pointer but with a left shift
                // of 256 (1 byte) - 8 (1 ASCII char) = 248 bits

Fixed code:
---
'openzeppelin-solidity': patch
---

`Base64`: Fix issue where dirty memory located just after the input buffer is affecting the result.
// SPDX-License-Identifier: MIT

pragma solidity ^0.8.20;

import {Base64} from "../utils/Base64.sol";

contract Base64Dirty {
    struct A {
        uint256 value;
    }

    function encode(bytes memory input) public pure returns (string memory) {
        A memory unused = A({value: type(uint256).max});
        // To silence warning
        unused;

        return Base64.encode(input);
    }
}
            let resultPtr := add(result, 0x20)
            let dataPtr := data
            let endPtr := add(data, mload(data))

            // In some cases, the last iteration will read bytes after the end of the data. We cache the value, and
            // set it to zero to make sure no dirty bytes are read in that section.
            let afterPtr := add(endPtr, 0x20)
            let afterCache := mload(afterPtr)
            mstore(afterPtr, 0x00)

                // To write each character, shift the 3 byte (24 bits) chunk
                // and apply logical AND with 0x3F to bitmask the least significant 6 bits.
                // Use this as an index into the lookup table, mload an entire word
                // so the desired character is in the least significant byte, and
                // mstore8 this least significant byte into the result and continue.
            // Reset the value that was cached
            mstore(afterPtr, afterCache)


  it('Encode reads beyond the input buffer into dirty memory', async function () {
    const mock = await ethers.deployContract('Base64Dirty');
    const buffer32 = ethers.id('example');
    const buffer31 = buffer32.slice(0, -2);

    expect(await mock.encode(buffer31)).to.equal(ethers.encodeBase64(buffer31));
    expect(await mock.encode(buffer32)).to.equal(ethers.encodeBase64(buffer32));
  });