CVE-2026-33671: Picomatch has a ReDoS vulnerability via extglob quantifiers

### Impact `picomatch` is vulnerable to Regular Expression Denial of Service (ReDoS) when processing crafted extglob patterns. Certain patterns using extglob quantifiers such as `+()` and `*()`, especially when combined with overlapping alternatives or nested extglobs, are compiled into regular expressions that can exhibit catastrophic backtracking on non-matching input. Examples of problematic patterns include `+(a|aa)`, `+(*|?)`, `+(+(a))`, `*(+(a))`, and `+(+(+(a)))`. In local reproduction, these patterns caused multi-second event-loop blocking with relatively short inputs. For example, `+(a|aa)` compiled to `^(?:(?=.)(?:a|aa)+)$` and took about 2 seconds to reject a 41-character non-matching input, while nested patterns such as `+(+(a))` and `*(+(a))` took around 29 seconds to reject a 33-character input on a modern M1 MacBook. Applications are impacted when they allow untrusted users to supply glob patterns that are passed to `picomatch` for compilation or matching. In those cases, an attacker can cause excessive CPU consumption and block the Node.js event loop, resulting in a denial of service. Applications that only use trusted, developer-controlled glob patterns are much less likely to be exposed in a security-relevant way. ### 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: - disable extglob support for untrusted patterns by using `noextglob: true` - reject or sanitize patterns containing nested extglobs or extglob quantifiers such as `+()` and `*()` - enforce strict allowlists for accepted pattern syntax - run matching in an isolated worker or separate process with time and resource limits - apply application-level request throttling and input validation for any endpoint that accepts glob patterns ### Resources - Picomatch repository: https://github.com/micromatch/picomatch - `lib/parse.js` and `lib/constants.js` are involved in generating the vulnerable regex forms - Comparable ReDoS precedent: CVE-2024-4067 (`micromatch`) - Comparable generated-regex precedent: CVE-2024-45296 (`path-to-regexp`)