CVE-2021-29399: XMB is vulnerable to cross-site scripting (XSS) due to inadequate filtering of BBCode input

Routine

MEDIUM 6.1UPGRADE

CVE-2021-29399 is a medium-severity flaw (CVSS 6.1) affecting xmb. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

XMB is vulnerable to cross-site scripting (XSS) due to inadequate filtering of BBCode input. This bug affects all versions of XMB. All XMB installations must be updated to versions 1.9.12.03 or 1.9.11.16.

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	0.8% (top 43%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-04-19
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: xmbforum2

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

Am I affected?

Timeline

2021-04-19 12:15 UTCPublished CVE record published
2026-06-17 03:47 UTCUpdated Record last modified

xmbforum2 xmb UPGRADE

Affected: >= 1.9.1 and < 1.9.11.16 · >= 1.9.11 and < 1.9.11.16 · >= 1.9.12 and < 1.9.12.03

Fixed in: 1.9.11.16, 1.9.12.03

Safe to downgrade to: a release before 1.9.1

1. Check installed version

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

2. UPGRADE to 1.9.11.16 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade xmb

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 1.9.1 (Debian / Ubuntu)

apt-cache madison xmb sudo apt install xmb=<VERSION_BEFORE_1.9.1> sudo apt-mark hold xmb

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

dnf --showduplicates list xmb sudo dnf downgrade xmb-<VERSION_BEFORE_1.9.1> sudo dnf versionlock add xmb

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-2021-29399?

xmb: upgrade to 1.9.11.16, 1.9.12.03. Exact commands for each OS are on this page.

Is CVE-2021-29399 being exploited?

CVE-2021-29399 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-2021-29399 affect?

CVE-2021-29399 affects xmb. Severity is medium (CVSS 6.1). XMB is vulnerable to cross-site scripting (XSS) due to inadequate filtering of BBCode input. This bug affects all versions of XMB. All XMB installations must be updated to versions 1.9.12.03 or 1.9.11.16.

How urgent is CVE-2021-29399?

Priority 36/100. No elevated risk signals yet.

References

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