File disclosure and SSRF via unescaped LESS values
Published Sep 11, 2026 · Updated Sep 11, 2026
SSTI in the Theme Customizer in Concrete CMS 9.0.0 through 9.5.2 allows remote authenticated users to read server files. ColorStyle and sibling Style classes interpolate submitted style properties into server-compiled LESS without neutralizing LESS syntax, permitting injected @import directives. Theme Customization permission is required; disclosed file contents enter the public CSS cache, and PHP stream wrappers also permit requests to internal resources.
Summary
What happened
SSTI in the Theme Customizer in Concrete CMS 9.0.0 through 9.5.2 allows remote authenticated users to read server files. ColorStyle and sibling Style classes interpolate submitted style properties into server-compiled LESS without neutralizing LESS syntax, permitting injected @import directives. Theme Customization permission is required; disclosed file contents enter the public CSS cache, and PHP stream wrappers also permit requests to internal resources.
The record
- CVE
- CVE-2026-81910
- Published
- Sep 11, 2026
- Updated
- Sep 11, 2026
- Vendor
- Concrete CMS
- Product
- Concrete CMS
- Classifications
- T1005
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 11, 2026CVE publishedPublication date reported by the CVE source.
- Sep 11, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=9.0.0 <=9.5.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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