EUVD-2026-76193
GHSA-77q8-j8j6-95hj
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network exploitation via web UI requires High privileges (Theme Customization role); only confidentiality impacted via arbitrary file read; no scope change or integrity/availability impact.
Primary rating from Vendor (ConcreteCMS).
CVSS VectorVendor: ConcreteCMS
Lifecycle Timeline
1DescriptionCVE.org
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.
AnalysisAI
Server-Side Template Injection in Concrete CMS 9 through 9.5.2 allows a privileged user holding the Theme Customization permission to inject arbitrary LESS directives into style values processed by the server-side LESS compiler. By crafting an @import (inline) directive within color, font, or image style fields, the attacker can read arbitrary files from the server filesystem and reach internal network resources via PHP stream wrappers, with the compiled output - including any exfiltrated file contents - written directly to the publicly accessible CSS cache. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires an authenticated CMS account with the 'Theme Customization' permission explicitly granted in Concrete CMS - this is a non-default, operator-assigned privilege typically held by site designers or administrators, not anonymous users or standard editors. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-assigned CVSS 4.0 score of 5.9 (Medium) is calibrated appropriately: PR:H correctly captures that exploitation requires Theme Customization permission, a non-default privilege not typically granted to untrusted users, and AT:P confirms a specific precondition - active LESS compilation in the Theme Customizer pipeline. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: Concrete CMS 9.5.3. … Detailed patch versions, workarounds, and compensating controls in full report. |
Threat intelligence, references, and detailed analysis are available after sign-in.
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