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Response snapshot Oct 27, 2026, 16:01 UTC

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VulnerabilityCVE-2026-114614

Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP URLs to non-loopback hosts

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.

Published Updated

At a glance

Exploited
Not known
Severity
2.6 Low (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: authlib: 1.8.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-jj7h-c3hg-m23x (opens a new tab)

What happened

### 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:

Continue reading

```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/cb` therefore has userinfo `localhost:80` and host `evil.example`.

Because the check is a raw prefix match against the full URL string, the `http://localhost:` prefix matches the userinfo portion and the function returns `True` even though the scheme is `http` and the host is an arbitrary external name. The trailing `:` in each allow-list entry — presumably intended to force a `host:port` shape and reject `http://localhost.evil.

com` — is also satisfied by the `user:password` separator inside userinfo, so `http://localhost:@evil.example/` matches too. The same construction works against all three loopback prefixes (`http://127.0.0.1:...@evil.example/`, `http://[::1]:...@evil.example/`).

`is_secure_transport()` is consumed at the following locations in v1.7.2, none of which independently reject URLs containing a userinfo component:

- `authlib/oidc/rpinitiated/registration.py:50-57` — validation of `post_logout_redirect_uris` during OIDC dynamic client registration for public clients (`token_endpoint_auth_method == "none"`). The preceding `is_valid_url()` check (`authlib/common/urls.py:142-146`) only requires `parsed.scheme and parsed.hostname` and does **not** reject userinfo, so the crafted URL passes both guards.

A public client can therefore register `http://localhost:80@attacker.example/cb` as a post-logout redirect target; the OpenID Provider will later 302 the end-user's browser to that cleartext non-loopback URL (carrying `state`). - `authlib/oauth2/rfc8414/models.

py:61,75,100,115,123,248,284` — validation of `issuer`, `authorization_endpoint`, `token_endpoint`, `jwks_uri`, `registration_endpoint`, `revocation_endpoint`, `introspection_endpoint` in Authorization Server Metadata / OIDC Discovery documents. A relying party using `AuthorizationServerMetadata.validate()` would accept endpoint values of this form as satisfying the "MUST use https" requirement when they do not.

- `authlib/oidc/rpinitiated/discovery.py:12` — validation of `end_session_endpoint` in provider metadata. - `authlib/oauth2/rfc6749/errors.py:64` and `authlib/oauth1/rfc5849/errors.py:33` — governs how `redirect_uri` is rendered in error bodies (cosmetic).

The `http://localhost:` prefix was introduced in commit `0225c86b` (first released in v0.13); `http://127.0.0.1:` and `http://[::1]:` were added later in the 1.6.x line. All variants share the same prefix-match weakness.

### PoC Against the current latest release (1.7.2):

```sh python3 -m venv venv ./venv/bin/pip install 'authlib==1.7.2' ./venv/bin/python poc.py ```

`poc.py`:

```python #!/usr/bin/env python3 """ is_secure_transport() must return True only for https:// URLs, or http:// URLs whose host is a loopback address (localhost / 127.0.0.1 / ::1).

Bypass: http://localhost:80@evil.example/cb has host 'evil.example' (userinfo = 'localhost:80') per RFC 3986, but matches the prefix 'http://localhost:' and is therefore accepted as secure. """ from urllib.parse import urlparse from authlib.common.security import is_secure_transport

cases = [ "http://localhost:80@evil.example/cb", "http://127.0.0.1:80@evil.example/cb", "http://localhost:@evil.example/cb", ]

vulnerable = False for url in cases: parsed = urlparse(url) ok = is_secure_transport(url) print(f"is_secure_transport({url!r}) = {ok} " f"[actual host = {parsed.hostname!r}, scheme = {parsed.scheme!r}]") if ok and parsed.hostname not in ("localhost", "127.0.0.1", "::1") and parsed.scheme != "https": vulnerable = True

if vulnerable: print("\nVULNERABLE: is_secure_transport() returned True for a plain-HTTP " "URL whose host is NOT a loopback address.") else: print("\nNOT VULNERABLE")

assert vulnerable, "expected bypass not observed" ```

Expected output:

``` is_secure_transport('http://localhost:80@evil.example/cb') = True [actual host = 'evil.example', scheme = 'http'] is_secure_transport('http://127.0.0.1:80@evil.example/cb') = True [actual host = 'evil.example', scheme = 'http'] is_secure_transport('http://localhost:@evil.example/cb') = True [actual host = 'evil.example', scheme = 'http']

VULNERABLE: is_secure_transport() returned True for a plain-HTTP URL whose host is NOT a loopback address. ```

### Impact Deployments are affected if they rely on `is_secure_transport()` — directly or via the Authlib call sites listed above — to reject cleartext non-loopback URLs supplied by an external party. The most realistic path is an OpenID Provider that enables OIDC dynamic client registration and RP-Initiated Logout: a public client can register a `post_logout_redir

Affected package ranges reported by GitHub: authlib: <= 1.7.2

Scores and how they were measured

CVSS base severity

2.6

Version 3.1As of

CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:N/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-jj7h-c3hg-m23x (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-jj7h-c3hg-m23x, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP URLs to non-loopback hosts (CVE-2026-114614). https://kevwire.com/record/CVE-2026-114614

MLA

"Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP URLs to non-loopback hosts (CVE-2026-114614)." KEVWire, 27 Oct. 2026, kevwire.com/record/CVE-2026-114614.

Chicago

KEVWire. "Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP URLs to non-loopback hosts (CVE-2026-114614)." Last modified October 27, 2026. https://kevwire.com/record/CVE-2026-114614.

Evidence summary (plain text)

Authlib: is_secure_transport() loopback exemption can be bypassed with a userinfo component, allowing cleartext-HTTP URLs to non-loopback hosts (Oct 27, 2026).
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 )
```
CVSS 2.6 (version 3.1; evidence as of Oct 27, 2026; https://github.com/advisories/GHSA-jj7h-c3hg-m23x).
Sources:
GitHub-reviewed advisory GHSA-jj7h-c3hg-m23x: https://github.com/advisories/GHSA-jj7h-c3hg-m23x
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-114614.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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