CVE-2026-35055: XenForo before 2.3.9 and before 2.2.18 is vulnerable to cross-site scripting (XSS) related to lightbox usage i

Routine

MEDIUM 6.1UPGRADE

CVE-2026-35055 is a medium-severity flaw (CVSS 6.1) affecting xenforo. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

XenForo before 2.3.9 and before 2.2.18 is vulnerable to cross-site scripting (XSS) related to lightbox usage in posts. An attacker can inject malicious scripts that execute when users interact with post content displayed in the lightbox.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-04-01
Last modified	2026-06-17

Publisher (CNA): VulnCheck · Vendor: xenforo

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-01 01:16 UTCPublished CVE record published
2026-06-17 10:40 UTCUpdated Record last modified

xenforo xenforo UPGRADE

Affected: < 2.2.18 · >= 2.3.0 and < 2.3.9

Fixed in: 2.2.18, 2.3.9

Safe to downgrade to: a release before 2.3.0

1. Check installed version

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

2. UPGRADE to 2.2.18 (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.

3. If no update is available yet, DOWNGRADE to a release before 2.3.0 (Debian / Ubuntu)

apt-cache madison xenforo sudo apt install xenforo=<VERSION_BEFORE_2.3.0> sudo apt-mark hold xenforo

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list xenforo sudo dnf downgrade xenforo-<VERSION_BEFORE_2.3.0> sudo dnf versionlock add xenforo

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2026-35055?

xenforo: upgrade to 2.2.18, 2.3.9. Exact commands for each OS are on this page.

Is CVE-2026-35055 being exploited?

CVE-2026-35055 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-2026-35055 affect?

CVE-2026-35055 affects xenforo. Severity is medium (CVSS 6.1). XenForo before 2.3.9 and before 2.2.18 is vulnerable to cross-site scripting (XSS) related to lightbox usage in posts. An attacker can inject malicious scripts that execute when users interact with post content displayed in the lightbox.

How urgent is CVE-2026-35055?

Priority 22/100. No elevated risk signals yet.

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References

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