Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP URLs to non-loopback hosts
- Published
- Last modified
- Status
- published
- Known exploitation
- Not listed in CISA KEV
- Public exploit
- None on Exploit-DB
Summary
Authlib, a Python library for building OAuth and OpenID Connect servers, is affected through its transport security check (is_secure_transport). An attacker who can supply a URL to certain OAuth/OIDC features, such as logout registration or metadata validation, can get a cleartext HTTP address accepted as if it were a local loopback address, leading to unencrypted redirects or acceptance of insecure endpoints.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original description
Authlib is a Python library which builds OAuth and OpenID Connect servers. From 0.13 until 1.8.0, authlib.common.security.is_secure_transport() uses a textual prefix comparison for loopback HTTP exemptions, so a URL whose userinfo begins with a loopback host can be accepted even when its parsed host is an external non-loopback system. An external party able to supply a URL to OIDC RP-Initiated Logout registration, authorization-server metadata validation, or another call site can bypass the TLS-required guard and cause cleartext redirection or acceptance of cleartext endpoints. The issue does not bypass redirect URI exact matching and does not by itself forge tokens or authenticate users. The vulnerable authlib.common.security.is_secure_transport() implementation in authlib/common/security.py misinterprets the userinfo component before OIDC RP-Initiated Logout dynamic client registration and other consumers enforce transport security. This issue is fixed in version 1.8.0.
Affected versions
- authlib authlib
fixed in 1.8.0