Access control bypass via parameterized middleware prefixes
Published May 26, 2026 · Updated May 26, 2026
Access control bypass in Koa.js @koa/router 14.0.0 through versions before 15.0.0 allows remote attackers to skip route middleware. The v14 Layer pathAsRegExp default sends .use() paths directly to RegExp instead of path-to-regexp, so parameter tokens fail to match and the middleware chain is dropped. Applications are exposed only when a router prefix or .use() path contains a path parameter and skipped middleware enforces authentication, authorization, rate limits, or input sanitization.
Summary
What happened
Access control bypass in Koa.js @koa/router 14.0.0 through versions before 15.0.0 allows remote attackers to skip route middleware. The v14 Layer pathAsRegExp default sends .use() paths directly to RegExp instead of path-to-regexp, so parameter tokens fail to match and the middleware chain is dropped. Applications are exposed only when a router prefix or .use() path contains a path parameter and skipped middleware enforces authentication, authorization, rate limits, or input sanitization.
The record
- CVE
- CVE-2026-9495
- Published
- May 26, 2026
- Updated
- May 26, 2026
- Vendor
- Koa.js
- Product
- @koa/router
- Classifications
- CWE-284, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 26, 2026CVE publishedPublication date reported by the CVE source.
- May 26, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=14.0.0 <15.0.0
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- Parameterized .use() middleware bypass reproductionproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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