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

> Attackers can reuse OAuth2 authorization codes to obtain unauthorized access tokens, bypassing single-use restrictions and potentially taking over user accounts.

- **Severity:** Critical 9.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Sep 2026
- **Updated:** 1 Oct 2026
- **Also known as:** GHSA-mrq5-6m75-wpj5

## What is CVE-2026-73311?

CVE-2026-73311 is a critical authentication bypass vulnerability in XenForo, published on 8 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-294 (Authentication Bypass by Capture-replay)

## Which versions are affected by CVE-2026-73311?

It affects 1 product.


Products: Xenforo Xenforo.

## How do I fix CVE-2026-73311?

No fix has been published for CVE-2026-73311 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-73311 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73311 exists.

Public exploit code:

- Sanitized XenForo write-up and proof of concept for CVE-2026-73311. (github_poc): https://github.com/BomboBombone/CVE-2026-73311

## Other vulnerabilities in XenForo

- [CVE-2025-71279](https://insights.sbomify.com/CVE-2025-71279/): XenForo Passkey Security Bypass (critical 9.3)
- [CVE-2026-73309](https://insights.sbomify.com/CVE-2026-73309/): XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint (critical 9.1)
- [CVE-2026-73312](https://insights.sbomify.com/CVE-2026-73312/): XenForo < 2.3.13 Refresh Token Replay via Expired Access Token (critical 9.1)
- [CVE-2024-38457](https://insights.sbomify.com/CVE-2024-38457/): Xenforo before 2.2.16 allows CSRF. (high 8.8)
- [CVE-2024-38458](https://insights.sbomify.com/CVE-2024-38458/): Code injection in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-73311 and fix it if it is affected.

What it is: CVE-2026-73311 is a critical authentication bypass vulnerability in XenForo, published on 8 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73311 exists.

Affected product: XenForo. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-73311/ (Markdown: https://insights.sbomify.com/CVE-2026-73311/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-73311
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-73311
- OSV: https://osv.dev/vulnerability/CVE-2026-73311

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-73311/
Summaries are generated and may contain mistakes; the official description above is the record.