---
id: "CVE-2026-114617"
kind: "vulnerability"
aliases: ["CVE-2026-114617"]
title: "Authlib: ID token replay possible when nonce check is skipped"
severity: "medium"
cvss: 4.2
epss: 0.00188
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["authlib", "oauth", "openid-connect", "package", "python"]
not_affected_if: ["authorization-code-flow-only", "no-external-id-tokens"]
published_at: "2026-10-22T22:18:04+00:00"
first_seen_at: "2026-10-23T21:57:32+00:00"
updated_at: "2026-10-25T04:41:21+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-114617", "first_seen_at": "2026-10-23T21:57:32+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-114617", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# Authlib: ID token replay possible when nonce check is skipped

Authlib's OpenID Connect parser lets a token disable its own nonce check by setting nonce_supported to false. An attacker holding a validly signed ID token can replay it into their own session in implicit and hybrid flows.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `pip show authlib` and check the installed version is below `1.9.0`
- Search requirements or lock files for `authlib` to find pinned versions
- Check whether the app uses implicit or hybrid OpenID Connect flows, or accepts externally supplied ID tokens

## Fix

- Upgrade Authlib to `1.9.0` or later
- Until upgraded, avoid implicit and hybrid flows and do not accept externally supplied ID tokens

## Timeline

- 2026-10-23T21:57:32+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-114617
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-114617

## From the sources

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, OpenIDMixin.parse_id_token() reads the nonce_supported decision from the untrusted ID token being validated and sets the expected nonce to null when that claim is the JSON boolean false. In implicit and hybrid relying parties, or applications that directly accept externally supplied ID tokens, an attacker with a captured validly signed token can bypass the nonce-to-session binding and replay the victim's token into an attacker-controlled session. Plain authorization code flow is not affected, and the token must still pass signature, issuer, and audience validation. OpenIDMixin.parse_id_token() trusts nonce_supported in both authlib/integrations/base_client/sync_openid.py and authlib/integrations/base_client/async_openid.py to disable the expected nonce. This issue is fixed in version 1.9.0.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_