Low · CVSS 2.1CVE-2026-81925

Concrete CMS below 9.5.3 is vulnerable to Reflected Cross-Site Scripting (XSS) via Conversation Custom Date FormatCVE-2026-81925

Answer in brief

CVE-2026-81925 records a Low severity (CVSS 2.1) vulnerability in Concrete CMS below 9.5.3 is vulnerable to Reflected Cross-Site Scripting (XSS) via Conversation Custom Date Format. The current sources do not mark it as known exploited. The current feed maps Concrete CMS/Concrete CMS (generic), Concrete CMS/Concrete CMS (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 15, 2026Updated Sep 21, 2026Source checked Oct 30, 2026First seen by HOL Sep 15, 2026Material review Sep 21, 2026

Upstream Advisory

Key facts

Risk: Low · CVSS 2.1
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Not reported

Why this deserves its current priority

CVSS is 2.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Concrete CMS/Concrete CMS (generic), Concrete CMS/Concrete CMS (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:a:concretecms:concrete_cms::::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Concrete CMS/Concrete CMSgeneric	5.0.0	Not reported
Concrete CMS/Concrete CMSgeneric	>=5.0.0 <=9.5.2	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Concrete CMS/Concrete CMS, Concrete CMS/Concrete CMS.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 15, 2026

Sources and claim methodology

Source referencedocumentation.concretecms.org

Upstream source description

Concrete CMS before 9.5.3 improperly neutralized a user-supplied custom date format when rendering conversation messages, resulting in reflected cross-site scripting. An attacker could execute arbitrary JavaScript in the browser of a user who was tricked into submitting a crafted POST request to the conversation view endpoint. Exploitation was aided by the absence of a CSRF token on the endpoint, which allowed the payload to be delivered through an auto-submitting cross-origin POST without authentication. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.1 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.

Quoted source text, attributed separately from HOL analysis.