Contao Comments Bundle: Cross-site scripting in comment metadata
Summary
The Contao comments bundle does not sufficiently encode the email and website values of visitor comments when it renders them in the back end. An unauthenticated visitor can submit a comment with manipulated metadata. When a back-end user opens the Comments module, the script runs in the Contao back-end origin under that user's session, which can allow actions such as creating administrators or editing templates. Unpublished comments are also shown to moderators, so moderation does not prevent exposure.
Affected
- Contao 4.0.0 up to but excluding 5.3.50
- Contao 5.4.0-RC1 (Packagist lists 5.4.0) up to but excluding 5.7.12
Fixed in
- Contao 5.3.50
- Contao 5.7.12
The latest 5.3.x or 5.7.x release should be used.
Workaround
- Disable front-end comments until the update is applied, as suggested in the earlier vendor notice.
- No other vendor-approved workaround known.
Exploitation
- No public proof of concept found.
- No evidence of exploitation in the wild found; status unknown, not confirmed absent.
- CISA SSVC (per CNA): exploitation none, automatable no, technical impact total.
Our recommendation
- Inventory Contao installations and check whether the comments bundle is installed and comments are enabled.
- Upgrade to 5.3.50 or 5.7.12 or a newer release. If patching is delayed, disable front-end comments.
- On unpatched systems, check whether back-end users opened the Comments module since 25 August 2026, and review recently created admin accounts and changed templates.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Contao security advisory GHSA-628f-v4f6-p37r (GitHub) github.com
- Contao fix commit 22505d5 (GitHub) github.com
- Contao release 5.3.50 (GitHub) github.com
- Contao release 5.7.12 (GitHub) github.com
- Contao security advisory: Cross-site scripting in the comments bundle (contao.org) contao.org
- GitHub advisory GHSA-628f-v4f6-p37r github.com
- OSV GHSA-628f-v4f6-p37r osv.dev
- VulDB entry 416002 vuldb.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 02:37.
Original description (NVD)
Contao is an Open Source CMS. From version 4.0.0 until 5.3.50 and 5.7.12, an unauthenticated visitor can submit a comment whose email or website metadata is rendered without sufficient attribute and URL encoding by listComments() in comments-bundle/contao/dca/tl_comments.php. When a backend user opens the Comments module, attacker-controlled script can execute in the Contao backend origin under that user's session. Unpublished comments remain visible to moderators, so moderation does not prevent exposure. This issue is fixed in versions 5.3.50 and 5.7.12.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.