Cyber Resilience

CVE-2026-73309

Xenforo ≤ 2.3.13

Public PoC
Published
08 September 2026
Modified
11 September 2026
CVSS Score v4 9.1
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/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:X/V:X/RE:X/U:X
EPSS Score 0.0048 40th percentile
Risk Priority 37 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-73309 is a critical-severity Incorrect Comparison (CWE-697) vulnerability in Xenforo Xenforo. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Obfuscated Files or Information (T1027); ranked at the 40th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and AC-25 (Reference Monitor) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain valid token pairs by submitting empty values for client_secret and code_verifier parameters. Attackers can exploit PHP truthy evaluation logic, which treats…

more

empty strings as false and skips client secret validation and PKCE code verifier validation, to exchange a valid authorization code for a token pair without proving client identity or holding the PKCE commitment.

CWE(s)
CWE-697

Related Threats

MITRE ATT&CK Enterprise Techniques

T1027 Obfuscated Files or Information Stealth
Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-73310Same product: Xenforo Xenforo
CVE-2025-71278Same product: Xenforo Xenforo
CVE-2026-73313Same product: Xenforo Xenforo
CVE-2024-38458Same product: Xenforo Xenforo
CVE-2025-71281Same product: Xenforo Xenforo
CVE-2026-35056Same product: Xenforo Xenforo
CVE-2025-71279Same product: Xenforo Xenforo
CVE-2026-74239Same product: Xenforo Xenforo
CVE-2024-25006Same product: Xenforo Xenforo
CVE-2024-38457Same product: Xenforo Xenforo

Affected Assets

xenforo
xenforo
≤ 2.3.13

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation directly exercises security-relevant comparisons to discover incorrect logic.

AC-25 Reference Monitor partial match

A reference monitor must be small and correct, structurally limiting the chance of flawed comparison logic in authorization decisions.

SA-8 Security and Privacy Engineering Principles partial match

Security engineering principles require correct implementation of comparison logic used for access and authentication decisions.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 partial match
prevents

Secure development practices directly require correct logic for security comparisons and thereby prevent this class of flaw.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle includes code review and testing that can catch incorrect comparison logic.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate correct comparison logic for security decisions.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles can require robust comparison mechanisms for access decisions.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly address avoiding incorrect comparison operators and logic.

A.8.29 Security testing in development and acceptance partial match
finds

Security testing can detect incorrect comparison flaws before deployment.

A.8.5 Secure authentication partial match
degrades

Secure authentication mechanisms rely on correct comparison of credentials or tokens.

References