High Integrity exploit reference

CVE-2026-73316 — XenForo < 2.3.13 Payment Replay via PayPal REST Payment Provider

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. Attackers can replay a valid webhook payload to trigger duplicate payment events, resulting in repeated subscription activations and unauthorized account upgrades.

Published Sep 8, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulnCheck

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.3% (30-day exploitation probability)+3
Technical severity (high)+6
CISA SSVC: exploitation "poc"+5
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.27%

ahead of 17% of scored CVEs · Oct 15, 2026

Affects

Xenforo

CVSS base

7.5

High · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Proof of concept

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Xenforo Xenforo).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (integrity), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Xenforo	Xenforo	< 2.3.13	Vulnerable	NIST National Vulnerability Database
Xenforo	Xenforo	< 2.3.13	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.7	CVSS 4.0	High	—	—	disclosure@vulncheck.com via NIST National Vulnerability Database
8.7	CVSS 4.0	High	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP
7.5	CVSS 3.1	High	3.9	3.6	disclosure@vulncheck.com via NIST National Vulnerability Database
7.5	CVSS 3.1	High	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N (score shown at the top: disclosure@vulncheck.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-345 · Insufficient Verification of Data Authenticity

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · xenforo/xenforo
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 7.5
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Sep 8, 2026 · VulnCheck

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

5 on the record

xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-g
Release Notes, vendor-advisory, patch, NIST National Vulnerability Database
xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-securi
Release Notes, release-notes, NIST National Vulnerability Database
www.vulncheck.com/advisories/xenforo-payment-replay-via-paypal-rest-payment-provider
Third Party Advisory, third-party-advisory, NIST National Vulnerability Database
github.com/BomboBombone/CVE-2026-73316
Exploit, Third Party Advisory, exploit, NIST National Vulnerability Database
bombobombone.github.io/posts/cve-2026-73316/
Exploit, Third Party Advisory, technical-description, NIST National Vulnerability Database

Elsewhere on this site

Xenforo
every CVE for this vendor

Integrity
same class

CWE-345
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-74239 XenForo < 2.3.13 Path Traversal via Style Archive Importer on Windows Sep 8, 2026
Low CVE-2026-73317 XenForo < 2.3.13 Missing Authorization via ACP Cache-Rebuild Dispatcher Sep 8, 2026
Low CVE-2026-73318 XenForo < 2.3.13 Missing Authorization via force-agreement Controller Sep 8, 2026
Medium CVE-2026-73319 XenForo < 2.3.13 XSS via Dynamic Redirect Handler Sep 8, 2026
Medium CVE-2026-73321 XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser Sep 8, 2026
Medium CVE-2026-73320 XenForo < 2.3.13 Unauthenticated Information Disclosure via Unfurl Endpoint Sep 8, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-73316 is "XenForo < 2.3.13 Payment Replay via PayPal REST Payment Provider", rated High. It affects Xenforo (Xenforo); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.27% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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