How severe is CVE-2021-40100?

CVE-2021-40100 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-40100 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40100?

CVE-2021-40100 affects Concretecms Concrete Cms. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40100?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-40100 published?

CVE-2021-40100 was published on 2021-09-24 and last updated on 2026-06-17.

CVE-2021-40100

CVE-2021-40100 is a medium-severity vulnerability in Concretecms Concrete Cms with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v2: 3.5
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Concretecms Concrete Cms
Published: 2021-09-24
Last modified: 2026-06-17

Description

An issue was discovered in Concrete CMS through 8.5.5. Stored XSS can occur in Conversations when the Active Conversation Editor is set to Rich Text.

Frequently asked questions

What is CVE-2021-40100?: An issue was discovered in Concrete CMS through 8.5.5. Stored XSS can occur in Conversations when the Active Conversation Editor is set to Rich Text.
How severe is CVE-2021-40100?: CVE-2021-40100 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-40100 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40100?: CVE-2021-40100 affects Concretecms Concrete Cms. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40100?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-40100 published?: CVE-2021-40100 was published on 2021-09-24 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:concretecms:concrete_cms:*:*:*:*:*:*:*:*

More vulnerabilities in Concretecms Concrete Cms

CVE-2023-48648 — Critical (CVSS 9.8): Concrete CMS before 8.5.13 and 9.x before 9.2.2 allows unauthorized access because directories can be created with…
CVE-2022-21829 — Critical (CVSS 9.8): Concrete CMS Versions 9.0.0 through 9.0.2 and 8.5.7 and below can download zip files over HTTP and execute code from…
CVE-2021-22958 — Critical (CVSS 9.8): A Server-Side Request Forgery vulnerability was found in concrete5 < 8.5.5 that allowed a decimal notation encoded IP…
CVE-2021-40098 — Critical (CVSS 9.8): An issue was discovered in Concrete CMS through 8.5.5. Path Traversal leading to RCE via external form by adding a…
CVE-2026-85385 — Critical (CVSS 9.6): Concrete CMS below 9.5.4 did not validate the user timezone value (uTimezone) on write and rendered it without output…
CVE-2022-30117 — Critical (CVSS 9.1): Concrete 8.5.7 and below as well as Concrete 9.0 through 9.0.2 allow traversal in /index.php/ccm/system/file/upload…

All CVEs affecting Concretecms Concrete Cms →

Other CWE-79 (Cross-site Scripting (XSS)) vulnerabilities

CVE-2026-106102 — Critical (CVSS 10.0): Quasar Framework is a framework for building high-performance Vue.js user interfaces. Prior to 2.22.0, the SSR-only…
CVE-2026-59167 — Critical (CVSS 10.0): SunEditor is a lightweight and powerful WYSIWYG editor in vanilla JavaScript with no dependencies. Prior to 2.47.11,…
CVE-2026-85061 — Critical (CVSS 10.0): MapLibre GL JS is an interactive vector tile map library for web browsers. Prior to 6.4.1, DOM.sanitize() in…
CVE-2025-49410 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Imran Emu TC…
CVE-2024-47875 — Critical (CVSS 10.0): DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG. DOMpurify was vulnerable to…
CVE-2024-6886 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Gitea…

Browse all CWE-79 (Cross-site Scripting (XSS)) vulnerabilities →