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Vulnerability record · CVE-2026-73314 · published 8 September 2026

CVE-2026-73314: Xenforo vulnerability

Xenforo · Xenforo

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. When the algorithm cannot be mapped to a supported hash function, the verification function incorrectly returns true instead of failing, causing the caller to treat the fabricated request as verified and process the payment event without a valid PayPal signature.

8.7 CVSS 4.0 High EPSS 0.65% · top 50.9% CWE-754 · CWE-754
8.7CVSS 4.0 base score
0.65%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
5References, 2 tagged exploit
11 Sep 2026Last modified by NVD

Description

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. When the algorithm cannot be mapped to a supported hash function, the verification function incorrectly returns true instead of failing, causing the caller to treat the fabricated request as verified and process the payment event without a valid PayPal signature.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bombobombone.github.io/posts/cve-2026-73314/ ExploitThird Party Advisory
https://github.com/BomboBombone/CVE-2026-73314 ExploitThird Party Advisory
https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-rest-webhook Third Party Advisory
https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.23 Release Notes
https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/ Release Notes

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.3CVE-2025-71279Xenforo improper authentication vulnerabilityXenForo before 2.3.7 contains a security issue affecting Passkeys that have been added to user accounts. An attacker may be able to compromise the se…EPSS 0.45%9.1CVE-2026-73311Xenforo authentication bypass by capture-replay vulnerabilityXenForo before 2.3.13 contains an OAuth2 authorization code reuse vulnerability that allows attackers to obtain unauthorized token pairs by submittin…EPSS 0.50%9.1CVE-2026-73312Xenforo authentication bypass by capture-replay vulnerabilityXenForo before 2.3.13 contains a refresh token replay vulnerability that allows attackers to reuse a refresh token multiple times by exploiting the f…EPSS 0.47%9.1CVE-2026-73309Xenforo vulnerabilityXenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain va…EPSS 0.69%8.8CVE-2024-38457Xenforo cross-site request forgery vulnerabilityXenforo before 2.2.16 allows CSRF.EPSS 7.4%8.8CVE-2024-38458Xenforo code injection vulnerabilityXenforo before 2.2.16 allows code injection.EPSS 0.89%8.7CVE-2026-73316Xenforo insufficient verification of data authenticity vulnerabilityXenForo before 2.3.13 contains a payment replay vulnerability in the PayPal REST payment provider that allows attackers to process the same webhook p…EPSS 0.27%8.7CVE-2025-71278Xenforo incorrect authorization vulnerabilityXenForo before 2.3.5 allows OAuth2 client applications to request unauthorized scopes. This affects any customer using OAuth2 clients on any version …EPSS 0.27%

Source: NIST National Vulnerability Database (record CVE-2026-73314), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.