CVE-2021-35955

lowpriority · track · 19EPSS 0.006 · 46 %ileEUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

0.56% (46th) EPSS

CVSS 3.5 · low

Is it mine?

10 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · nvd · osv

EPSS · scored 2026-10-27

Contao >=4.0.0 allows backend XSS via HTML attributes to an HTML field. Fixed in 4.4.56, 4.9.18, 4.11.7.

cvss

Technical severity, 0–10. One row per scoring source.

5.9

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · low–medium · 3.5–5.9

v2.03.5lowAV:N/AC:M/Au:S/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 6.8 · impact 2.9

v3.14.8mediumCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:Nprimary · NVD / NIST USexploitability 1.7 · impact 2.7

v3.15.9mediumCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:Lsecondary · OSV

v3.14.4mediumCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-79USprimaryCWE-79US

affected products (10)

Products and version ranges known to be affected.

n/a n/a≤ n/aenisa_euvdEU
contao contao4.0.0 → 4.4.56nvdUScpe:2.3:a:contao:contao:*:*:*:*:*:*:*:*
contao contao4.10.0 → 4.11.7nvdUScpe:2.3:a:contao:contao:*:*:*:*:*:*:*:*
contao contao4.5.0 → 4.9.18nvdUScpe:2.3:a:contao:contao:*:*:*:*:*:*:*:*
Packagist contao/contao4.0.0 → 4.4.56osvUSpkg:composer/contao/contao
Packagist contao/contao4.10.0 → 4.11.7osvUSpkg:composer/contao/contao
Packagist contao/contao4.5.0 → 4.9.18osvUSpkg:composer/contao/contao
Packagist contao/core-bundle4.0.0 → 4.4.56osvUSpkg:composer/contao/core-bundle
Packagist contao/core-bundle4.10.0 → 4.11.7osvUSpkg:composer/contao/core-bundle
Packagist contao/core-bundle4.5.0 → 4.9.18osvUSpkg:composer/contao/core-bundle

advisories (1)

Vendor and ecosystem advisories describing this.

GHSA-hr3h-x6gq-rqcpCross site scripting via HTML attributes in the back end2021-08-25ghsa · osvUS
### Impact It is possible for untrusted users to inject malicious code into HTML attributes in the back end, which will be executed both in the element preview (back end) and on the website (front end). Installations are only affected if there are untrusted back end users who have the rights to modify HTML fields (e.g. TinyMCE). ### Patches Update to Contao 4.4.56, 4.9.18 or 4.11.7 ### Workarounds Disable all fields that allow HTML for untrusted back end users or disable the login for these users. ### References https://contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end ### For more information If you have any questions or comments about this advisory, open an issue in [contao/contao](https://github.com/contao/contao/issues/new/choose). ### Credits Thanks to Mikhail Khramenkov and Moritz Vondano for reporting this security issue.

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd nvd osv NVD CVE.org MITRE

published 2021-08-12modified 2026-06-17

related (53,012)

Related entries.

ID	severity	EPSS	exploitable	published
CVE-2026-42897US	medium6.1OT critical	70.7% (99th)	KEV	2026-05-14
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network…
CVE-2025-66376US	medium6.1OT critical	20.2% (97th)	KEV	2026-01-05
Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
CVE-2025-68461US	medium6.1OT critical	27.4% (98th)	KEV	2025-12-18
Roundcube Webmail before 1.5.12 and 1.6 before 1.6.12 is prone to a Cross-Site-Scripting (XSS) vulnerability via the animate tag in an SVG document.
CVE-2025-48700US	—OT critical	1.71% (77th)	KEV	2025-06-23
An issue was discovered in Zimbra Collaboration (ZCS) 8.8.15 and 9.0 and 10.0 and 10.1. A Cross-Site Scripting (XSS) vulnerability in the Zimbra Classic UI allows attackers to exec…
CVE-2025-27915US	—OT critical	4.06% (91st)	KEV	2025-03-12
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient…

+53007 more

references (8)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan