CVE-2026-71209
Received Received - Intake

Authentication Bypass via Path Traversal in Audiobookshelf

Publication date: 2026-08-05

Last updated on: 2026-08-05

Assigner: 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c

Description
audiobookshelf's authentication-exemption check (server/routers/Auth.js) matches unauthenticated-allowed GET routes against req.path via a regex requiring a literal /items/:id/cover or /authors/:id/image shape, where req.path retains %2F sequences URL-encoded. Express's router decodes the :id route parameter before handler code runs, so a %2F-encoded '../' sequence in :id (e.g. ..%2f..%2f..%2ftmp%2fpwned) passes the literal-path auth-exemption check while resolving to a real path-traversal payload once decoded. CacheManager.handleCoverCache then joins this decoded value into a cache file path and streams the result before any database-backed ownership check. This bypasses the fix applied for CVE-2025-25205 (which anchored the exemption regex and switched it to req.path) and results in unauthenticated arbitrary file read of any file matching the pattern *_<width>[x<height>].<ext> that the service account can read.

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Meta Information

Published
2026-08-05
Last Modified
2026-08-05
Generated
2026-08-05
AI Q&A
2026-08-05
EPSS Evaluated
N/A
NVD
CVE-2026-71209
EUVD
EUVD-2026-53206

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
audiobookshelf audiobookshelf *
express express *
advplyr audiobookshelf From 2.17.0 (inc) to 2.19.0 (inc)
advplyr audiobookshelf 2.19.1

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-22 The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Attack-Flow Graph

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Executive Summary

CVE-2026-71209 is an authentication-bypass vulnerability in Audiobookshelf versions 2.17.0 through 2.19.0. It allows unauthenticated users to bypass security checks by including specific URL-encoded substrings like /items/:id/cover or /authors/:id/image. The flaw occurs because the regex pattern used to check unauthenticated routes does not properly account for URL-encoded characters, enabling path traversal attacks that read arbitrary files on the server.

The vulnerability stems from improperly anchored regex patterns in the authentication logic, which fail to block requests containing encoded sequences like %2F (slash) in route parameters. This bypasses intended access controls and allows unauthenticated file reads of files matching specific patterns.

Detection Guidance

Check for unauthenticated requests to endpoints like /api/items/1/cover or similar paths with encoded sequences such as %2F. Monitor logs for unusual file access patterns or requests containing ../ sequences in parameters. Ensure regex patterns in Auth.js are properly anchored and compare against req.path instead of req.originalUrl.

Impact Analysis

This vulnerability allows unauthenticated attackers to read arbitrary files on the server where Audiobookshelf is running. Attackers could access sensitive system files, user data, or application configurations. It may also enable reflective denial-of-service attacks or cause server crashes due to undefined user objects in downstream code.

The impact includes remote exploitation without authentication, trivial proof-of-concept attacks, and potential global server crashes. Attackers can exploit this to disclose sensitive information or disrupt service availability.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive personal data, violating GDPR and HIPAA requirements for data protection and access controls. Unauthorized file access may result in data breaches, triggering mandatory breach notifications and potential fines under these regulations.

Mitigation Strategies

Upgrade to Audiobookshelf version 2.19.1 or later to apply the patch. Review and update authentication logic to ensure regex patterns are anchored and compare against req.path. Restrict access to sensitive endpoints and monitor for unauthorized file access attempts.

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