Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-73311 – OAuth2 Authorization Code Reuse / Token Theft – XenForo before 2.3.13

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-73311 is an OAuth2 authorization code reuse vulnerability (CWE-294, Authentication Bypass by Capture-replay) affecting XenForo forum software before version 2.3.13. XenForo’s OAuth2 implementation fails to invalidate authorization codes after they are first exchanged for tokens, allowing a previously used code to be resubmitted to mint an additional, independent token pair for the same user and scopes. The flaw is rated CRITICAL (CVSS v4.0 base score 9.1); it also carries a CVSS v3.1 HIGH rating.

Technical details

  • Root cause: After a client exchanges an OAuth2 authorization code for an access/refresh token pair, XenForo does not mark that code as consumed or otherwise invalidate it.
  • Trigger condition: An attacker in possession of a previously issued (and already-used) authorization code can resubmit it to the token endpoint.
  • Attack vector: Network-based; no user interaction required; the OAuth2 authorization code flow’s single-use guarantee is bypassed by replaying a captured code.
  • Impact: The attacker obtains a fresh, unauthorized token pair scoped to the victim account, enabling unauthorized API access and potential account compromise.

Affected software

  • XenForo, all versions from the initial release up to (but not including) 2.3.13.

Severity

  • CVSS v3.1: 7.4 (HIGH) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
  • CVSS v4.0: 9.1 (CRITICAL) — 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

Mitigation and recommended actions

  • Immediate: Upgrade XenForo to version 2.3.13 or later, which corrects the authorization code invalidation logic.
  • If immediate patching isn’t possible: Monitor OAuth2 token issuance logs for repeated token grants against the same authorization code, and consider disabling/restricting OAuth2 client integrations until the update is applied. There is no vendor-documented workaround other than upgrading.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Raw response body: jQuery.extend(true, XenForo, Forum software by XenForo™, <!--XF:branding, <html id="XenForo", <html id="XF"
  • JavaScript object present once the page runs: XF.GuestUsername

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge