Vulnerability in Concrete CMS (CVE-2026-81910)
Summary
Vulnerability in Concrete CMS (CVE-2026-81910). Confidential information can be exposed externally.
Original description
The description as published by the source.
Concrete CMS 9 through 9.5.2 is vulnerable to Server-Side Template Injection (SSTI) in Theme Customizer via Unvalidated Style Values. Values submitted through the customizer (color channels and other style properties handled by ColorStyle and sibling Style classes such as FontFamilyStyle and ImageStyle) are interpolated into server-compiled LESS source without neutralization of LESS syntax, allowing a user with the Theme Customization permission to inject arbitrary LESS directives. By injecting the @import (inline) directive, an attacker can read arbitrary files on the server and reach internal network resources through PHP stream wrappers. The compiled output, including any disclosed file contents, is written to the site's publicly served CSS cache, exposing database credentials, private keys, and other application secrets, and enabling server-side request forgery. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.9 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-81910 has been found in Concrete CMS.
Confidential information can be exposed externally. CVSS score: 6.5/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Concrete CMS CVE-2026-81910" on the vendor's site.
CVE-2026-81910 (Concrete CMS) — CWE-1336 / CVSS v3 6.5
Attack vector: remote (network-reachable) / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-1336) exists in Concrete CMS.
Check the vendor advisory for the affected versions of Concrete CMS.
Severity: Medium (CVSS 6.5/10). Confidential information can be exposed externally.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで Concrete CMS を使っているサービスとバージョンを洗い出す。
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2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
References
- web documentation.concretecms.org
- web nvd.nist.gov
- web github.com