Picomatch: Method Injection in POSIX Character Classes causes incorrect Glob Matching
Date: 2026-03
Affected: npm/picomatch, npm/picomatch, npm/picomatch
Attack vector: auth-bypass
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-33672
CWE: CWE-1321
CVSS: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)

### Impact picomatch is vulnerable to a **method injection vulnerability (CWE-1321)** affecting the `POSIX_REGEX_SOURCE` object. Because the object inherits from `Object.prototype`, specially crafted POSIX bracket expressions (e.g., `[[:constructor:]]`) can reference inherited method names. These methods are implicitly converted to strings and injected into the generated regular expression. This leads to **incorrect glob matching behavior (integrity impact)**, where patterns may match unintended filenames. The issue does **not enable remote code execution**, but it can cause security-relevant logic errors in applications that rely on glob matching for filtering, validation, or access control. All users of affected `picomatch` versions that process untrusted or user-controlled glob patterns are potentially impacted. ### Patches This issue is fixed in picomatch 4.0.4, 3.0.2 and 2.3.2. Users should upgrade to one of these versions or later, depending on their supported release line. ### Workarounds If upgrading is not immediately possible, avoid passing untrusted glob patterns to picomatch. Possible mitigations include: - Sanitizing or rejecting untrusted glob patterns, especially those containing POSIX character classes like `[[:...:]]`. - Avoiding the use of POSIX bracket expressions if user input is involved. - Manually patching the library by modifying `POSIX_REGEX_SOURCE` to use a null prototype: ```js const POSIX_REGEX_SOURCE = { __proto__: null, alnum


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