CVE-2026-73314

XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook

Published Sep 8, 2026 CVSS 4.0 · 8.7 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:*
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Xenforo
Xenforo xenforo
Vendors & Products Xenforo
Xenforo xenforo
Type Values Removed Values Added
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.
Title XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook
Weaknesses CWE-754
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}

cvssV4_0

{'score': 8.7, 'vector': '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
VulnCheck
Published
Updated
Oct 1, 2026, 3:20 PM
Reserved
Aug 11, 2026, 7:56 PM
Status
Analyzed
Published
Sep 8, 2026, 2:17 PM
Modified
Sep 11, 2026, 8:31 PM