CVE-2026-107845: XSS (CVSS 9.3)

Description

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 Unpublished comments remain visible to moderators, so moderation does not prevent exposure.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.

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CVSS v3.1 Score

9.3

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0027

Probability of exploitation

0.18%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

CWE-116 CWE-116

References

Other References

https://github.com/contao/contao/commit/22505d5f79bc1a7f52e2cba5fddf6007e1f0408a https://github.com/contao/contao/releases/tag/5.3.50 https://github.com/contao/contao/releases/tag/5.7.12 https://github.com/contao/contao/security/advisories/GHSA-628f-v4f6-p37r

Frequently Asked Questions

What is CVE-2026-107845? +

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 Unpublished comments remain visible to moderators, so moderation does not prevent exposure.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. It has a CVSS v3.1 base score of 9.3 (CRITICAL).

How severe is CVE-2026-107845? +

CVE-2026-107845 has a CVSS v3.1 score of 9.3 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0027, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-107845? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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