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Path To RegexpApplication · Pillarjs

CVE-2026-4926

HIGH · 7.5 CVSS v3.1 Published 2026-03-26
Fix available
A fix is available. Upgrade to 8.4.0 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Impact: A bad regular expression is generated any time you have multiple sequential optional groups (curly brace syntax), such as `{a}{b}{c}:z`. The generated regex grows exponentially with the number of groups, causing denial of service. Patches: Fixed in version 8.4.0. Workarounds: Limit the number of sequential optional groups in route patterns. Avoid passing user-controlled input as route patterns.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A ReDoS vulnerability exists where multiple sequential optional groups using curly brace syntax (e.g., {a}{b}{c}:z) in route patterns cause the generated regular expression to grow exponentially. This leads to catastrophic backtracking during regex processing, causing denial of service.

MitigationUpgrade to version 8.4.0 which contains the patch. As a workaround, limit the number of sequential optional groups in route patterns and avoid passing user-controlled input directly as route patterns.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Path To RegexpApplication
Affected:>= 8.0.0, < 8.4.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed path-to-regexp version
    Run 'npm list path-to-regexp' in your project directory, or inspect package.json dependencies
    Affected if Version is >= 8.0.0 and < 8.4.0
  2. Verify path-to-regexp is used in the application
    Search source files for require('path-to-regexp') or import statements from 'path-to-regexp' or 'pillarjs/path-to-regexp'
    Affected if The application imports and uses path-to-regexp library
  3. Inspect route definitions for vulnerable curly brace patterns
    Search your route definition files for patterns containing multiple sequential optional groups in curly braces, such as {param1}{param2}{param3}:z or similar constructs
    Affected if Route patterns contain three or more sequential optional groups using curly brace syntax

You are affected if your project uses path-to-regexp version 8.0.0 through 8.3.x AND your codebase contains route definitions with multiple sequential optional groups using curly brace syntax like {a}{b}{c}:z.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 8.4.0 or later
Fixed in 8.4.0
Interim mitigation

Upgrade to version 8.4.0 which contains the patch. As a workaround, limit the number of sequential optional groups in route patterns and avoid passing user-controlled input directly as route patterns.

Recommended fix High confidence

8.4.0

  1. Check the current version of path-to-regexp in your project by reviewing package.json or running 'npm list path-to-regexp' or 'yarn list path-to-regexp'
  2. Upgrade path-to-regexp to version 8.4.0 or later using your package manager: 'npm install path-to-regexp@^8.4.0' or 'yarn upgrade path-to-regexp@^8.4.0'
  3. Run your test suite to verify the upgrade does not break existing functionality
  4. If you have routes using multiple sequential optional groups like {a}{b}{c}:z, verify they now generate safe regex patterns
  5. Deploy the updated application
Caveat No breaking changes documented for this release; the fix addresses the exponential regex growth issue

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Path To Regexp Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-4926 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data