CVE-2026-73309: XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows

Q: How do I fix CVE-2026-73309?

xenforo: upgrade to 2.3.13. Exact commands for each OS are on this page.

Q: Is CVE-2026-73309 being exploited?

CVE-2026-73309 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-73309 affect?

CVE-2026-73309 affects xenforo. Severity is high (CVSS 7.4). 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.

Q: How urgent is CVE-2026-73309?

Priority 49/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.4REMOTEUPGRADE

CVE-2026-73309 is a high-severity flaw (CVSS 7.4) affecting xenforo. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 empty strings as false and skips client secret validation and PKCE code verifier validation, to exchange a valid authorization code for a token pa

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.4 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 48%)
CISA exploited list	No
Weakness	CWE-697
Published	2026-09-08
Last modified	2026-09-11

Publisher (CNA): VulnCheck · Vendor: xenforo

Last updated 2026-09-11 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-08 14:17 UTCPublished CVE record published
2026-09-11 20:33 UTCUpdated Record last modified

xenforo xenforo UPGRADE

Affected: < 2.3.13

Fixed in: 2.3.13

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy xenforo || rpm -q xenforo || xenforo --version

2. UPGRADE to 2.3.13 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade xenforo

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade xenforo

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-73309?

xenforo: upgrade to 2.3.13. Exact commands for each OS are on this page.

Is CVE-2026-73309 being exploited?

CVE-2026-73309 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-73309 affect?

CVE-2026-73309 affects xenforo. Severity is high (CVSS 7.4). 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.

How urgent is CVE-2026-73309?

Priority 49/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

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References

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