SB2026110470 - Cross-site scripting in authlib

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Main Vulnerability Database SB2026110470

SB2026110470 - Cross-site scripting in authlib

Published: November 4, 2026

Security Bulletin ID SB2026110470
CSH Severity
Low
Patch available
YES
Number of vulnerabilities 1
Exploitation vector Remote access
Highest impact Data manipulation

Breakdown by Severity

Low 100%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 1 vulnerability.


1) Cross-site scripting (CVE-ID: N/A)

CWE-ID: CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSSv4: 2.1 [CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N]


The vulnerability allows a remote user to execute arbitrary JavaScript in the authorization server's origin, access sensitive same-origin data, and perform authenticated actions on behalf of a victim.

The vulnerability exists due to insufficient redirect URI scheme validation in Authlib's OAuth/OIDC client-registration validators when processing redirect metadata for web clients, allowing cross-site scripting through response_mode=form_post. A remote user can register a client with a javascript: redirect URI and induce a victim to authorize it to execute JavaScript in the authorization server's origin. The resulting form action javascript://host/%0Adocument.body.innerHTML=location.origin demonstrates the exploit: Chromium decodes %0A into a line feed, treats //host/ as a comment, and executes the following JavaScript.

Exploitation requires the server to register OpenIDImplicitGrant.


Remediation

Install update from vendor's website.

References