Cross site scripting in the system log

published 2021-06-23 5 y ago modified 2026-09-10 1 mo ago also GHSA-h58v-c6rf-g9f7 , EUVD-2021-1472

cvss: 6.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 54%
public exploits: 0; none known

Contao 4.5.x through 4.9.x before 4.9.16, and 4.10.x through 4.11.x before 4.11.5, allows XSS. It is possible to inject code into the tl_log table that will be executed in the browser when the system log is called in the back end.

Patch / fix

fixed in 3

packagist contao/core-bundle 4.9.16, 4.11.5
packagist contao/contao 4.9.16, 4.11.5
contao contao 4.9.16, 4.11.5

Exploit prediction

0.74% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:N/I:P/A:N
GitHub	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
packagist	contao/core-bundle	>=4.5.0, <4.9.16 >=4.10.0, <4.11.5	4.9.16 4.11.5
packagist	contao/contao	>=4.5.0, <4.9.16 >=4.10.0, <4.11.5	4.9.16 4.11.5

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

contao.org /en/security-advisories/cross-site-scripting-in-the-system-log-2021.html
web, vendor-advisory
github.com /contao/contao/security/advisories/GHSA-h58v-c6rf-g9f7
web, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2021-35210
advisory
github.com /FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2021-35210.yaml
web
github.com /FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2021-35210.yaml
web
github.com /contao/contao
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary