XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook
41Vexday Risk Score
No sign of exploitation. It has a public proof of concept.
ssvc Attendcvss 8.7epss 0.5%
exploitation probability
0.5%top 61% of all CVEs
observed exploitation
nono source reports it
1 public exploit(s)
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
Affected products
XenForo · XenForopublic PoCs found — 1
cve_referencegithub.com/BomboBombone/CVE-2026-73314★ 0⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.
References
https://bombobombone.github.io/posts/cve-2026-73314/https://github.com/BomboBombone/CVE-2026-73314https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-rest-webhookhttps://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/