CVE-2026-33671

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)

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.

A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.

CVE-2026-33671 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.0.4, 3.0.2, 2.3.2); upgrading removes the vulnerable code path.

Kodem intelligence

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.

1. What is CVE-2026-33671? CVE-2026-33671 is a high-severity inefficient regular expression (ReDoS) vulnerability in picomatch (npm), affecting versions >= 4.0.0, < 4.0.4. It is fixed in 4.0.4, 3.0.2, 2.3.2. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
2. How severe is CVE-2026-33671? CVE-2026-33671 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of picomatch are affected by CVE-2026-33671? picomatch (npm) versions >= 4.0.0, < 4.0.4 is affected.
4. Is there a fix for CVE-2026-33671? Yes. CVE-2026-33671 is fixed in 4.0.4, 3.0.2, 2.3.2. Upgrade to this version or later.
5. Is CVE-2026-33671 exploitable, and should I be worried? Whether CVE-2026-33671 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-33671 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-33671?
   • Upgrade picomatch to 4.0.4 or later
   • Upgrade picomatch to 3.0.2 or later
   • Upgrade picomatch to 2.3.2 or later