CVE-2026-73309
HighCVSS 7.4Summary
XenForo before version 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint. An unauthenticated attacker can obtain valid token pairs by submitting empty values for client_secret and code_verifier parameters, exploiting PHP truthy evaluation logic that treats empty strings as false and skips client secret and PKCE validation.
Risk Assessment
An attacker can hijack user sessions and gain unauthorized access to accounts, potentially leading to data theft or account takeover.
Recommendation
It is recommended to immediately upgrade XenForo to version 2.3.13 or later, which includes a fix for this vulnerability.
Other vulnerabilities in XenForo
See all- CVE-2026-74239High
XenForo before 2.3.13 contains a path traversal vulnerability in the style archive importer on Windows deployments that allows authenticated non-super administrators with style permissions to write arbitrary files outside the intended extraction directory by using backslash-based traversal sequences in ZIP member names.
- CVE-2026-73321Medium
XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authenticated attackers to cause persistent denial of service by submitting a post with deeply nested BBCode tags.
- CVE-2026-73320Medium
XenForo before 2.3.13 contains an unauthenticated information disclosure vulnerability that allows unauthenticated attackers to retrieve private unfurl records by supplying predictable auto-increment primary key IDs to the unfurl endpoint.
- CVE-2026-73319Medium
XenForo before 2.3.13 contains a cross-site scripting vulnerability in the dynamic redirect handler that allows unauthenticated attackers to execute arbitrary JavaScript in the board origin by crafting a malicious javascript: URI that bypasses host validation.
- CVE-2026-73318Low
XenForo before 2.3.13 contains a missing authorization vulnerability in the force-agreement controller that allows any ACP administrator to access and submit force-agreement forms regardless of their assigned permissions. Attackers can bypass the option permission declared in the navigation configuration to update the global policy last-updated timestamp, forcing all users to re-agree to the privacy policy or terms of service.
- CVE-2026-73317Low
XenForo before version 2.3.13 contains a missing authorization vulnerability in the ACP cache-rebuild dispatcher, allowing limited administrators with only the rebuildCache permission to perform unauthorized approval queue actions. Attackers can invoke the approval queue job under any user identity to approve queued registrations without required permissions, causing the moderation log to attribute actions to an impersonated account.
- CVE-2026-73316High
XenForo before 2.3.13 contains a payment replay vulnerability in the PayPal REST payment provider that allows attackers to process the same webhook payload multiple times by exploiting a missing duplicate transaction ID check.
- CVE-2026-73315High
XenForo before 2.3.13 contains a server-side request forgery vulnerability in the PayPal REST webhook handler that allows unauthenticated attackers to cause the server to make outbound HTTP requests to arbitrary destinations by supplying a crafted certificate URL in webhook headers without scheme, hostname, or allowlist validation.
- CVE-2026-73314High
XenForo before 2.3.13 contains a signature verification logic error in the PayPal REST webhook handler that allows unauthenticated attackers to bypass payment signature validation by submitting a webhook request with an unsupported auth_algo header value.
- CVE-2026-73313Medium
XenForo before 2.3.13 contains a multi-factor authentication bypass vulnerability in the passkey TFA provider that allows an authenticated attacker to complete login as another user by submitting their own registered passkey credential during the WebAuthn assertion step.
Original NVD description (English source)
XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain valid token pairs by submitting empty values for client_secret and code_verifier parameters. Attackers can exploit PHP truthy evaluation logic, which treats empty strings as false and skips client secret validation and PKCE code verifier validation, to exchange a valid authorization code for a token pair without proving client identity or holding the PKCE commitment.