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CVE-2026-114614 — Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP UR…

2026-11-02T05:21:57.541860+00:00

Affected: authlib

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.

GHSA-jj7h-c3hg-m23x — Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP UR…

2026-11-02T05:21:57.541925+00:00

Affected: PyPI: authlib

### Summary `authlib.common.security.is_secure_transport()` is used throughout Authlib to enforce the OAuth 2.0 / OIDC requirement that endpoint and redirect URIs use TLS, with an RFC 8252 §7.3 exemption for loopback `http://` URIs. The check is implemented as a textual `str.startswith` prefix match, so a URL such as `http://localhost:80@evil.example/cb` — whose actual host is `evil.example` and whose scheme is plain `http` — is accepted as "secure". An attacker who can supply a URL to any of the sinks that rely on this check (OIDC RP-Initiated Logout dynamic client registration, RFC 8414 authorization-server metadata validation, error-redirect rendering) can smuggle a cleartext non-loopback URL past the TLS-required guard. This is a defense-in-depth / spec-conformance failure; severity is low.

### Details **Affected versions:** `authlib >= 0.13, <= 1.7.2` (all releases containing the loopback prefix exemption; verified against 1.7.2, the current latest)

The vulnerable function, from `authlib/common/security.py` at v1.7.2:

```python 13 def is_secure_transport(uri): 14 """Check if the uri is over ssl.""" 15 if os.getenv("AUTHLIB_INSECURE_TRANSPORT"): 16 return True 17 18 uri = uri.lower() 19 return uri.startswith( 20 ("https://", "http://localhost:", "http://127.0.0.1:", "http://[::1]:") 21 ) ```

Per RFC 3986 §3.2 the authority component of a URI is `[ userinfo "@" ] host [ ":" port ]`. The URL `http://localhost:80@evil.example/…

PYSEC-2026-4354

2026-11-02T05:21:57.541998+00:00

Affected: PyPI: authlib