What’s Vulnerable › Vulnerabilities

CVE-2026-73314: XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-09-08 · updated 2026-09-11
• Weakness: CWE-754

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.

Affected products

• XenForo: before 2.3.13 — fixed in 2.3.13

How to fix

Upgrade to a fixed version: XenForo 2.3.13. Check the vendor advisory for mitigations.

References

• https://bombobombone.github.io/posts/cve-2026-73314/
• https://github.com/BomboBombone/CVE-2026-73314
• https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-rest-webhook
• 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/

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