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How the CVE Works:
The vulnerability arises due to insufficient server-side input sanitization in Umbraco CMS. An attacker with CMS edit privileges can craft a malicious payload using encoded JavaScript, bypassing client-side sanitization. When the payload is rendered on the front end, the script executes in the victim’s browser, leading to stored XSS. The server fails to detect the encoded payload, allowing persistent attack vectors such as session hijacking or phishing.
DailyCVE Form:
Platform: Umbraco CMS
Version: 9.x, 10.x
Vulnerability: Stored XSS
Severity: Critical
Date: 2023-05-15
What Undercode Say:
Exploitation:
1. Attacker logs into Umbraco backend.
- Inserts encoded JavaScript in content fields (e.g., rich text editor).
3. Payload persists in the database.
4. Victim views the page, triggering script execution.
Proof of Concept (PoC):
<img src=x onerror="alert('XSS')" />
Encoded variant:
&x3C;img src=x onerror=&x22;alert(&x27;XSS&x27;)&x22; /&x3E;
Detection:
Check for unsanitized user inputs in CMS render pipelines:
var sanitizer = new HtmlSanitizer(); var cleanHtml = sanitizer.Sanitize(userInput);
Mitigation:
1. Update to Umbraco 10.4.1+ or apply patches.
2. Implement server-side HTML encoding:
@Html.Raw(HttpUtility.HtmlEncode(untrustedContent))
3. Use Content Security Policy (CSP):
Content-Security-Policy: default-src 'self'; script-src 'unsafe-inline'
Analytics:
- Affected Versions: 9.0.0 to 10.4.0
- Attack Vector: Privileged CMS users
- CVSS Score: 9.1 (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H)
References:
References:
Reported By: https://github.com/advisories/GHSA-rhx4-hvx9-j387
Extra Source Hub:
Undercode
