CVE-2009-1070 in ExpressionEngine
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in system/index.php in ExpressionEngine 1.6.4 through 1.6.6, and possibly earlier versions, allows remote attackers to inject arbitrary web script or HTML via the avatar parameter.
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Analysis
by VulDB Data Team • 05/10/2025
The vulnerability identified as CVE-2009-1070 represents a critical cross-site scripting flaw within ExpressionEngine content management system versions 1.6.4 through 1.6.6, with potential prevalence in earlier releases. This security weakness resides in the system/index.php file and specifically targets the avatar parameter handling mechanism. The flaw enables remote attackers to execute malicious web scripts or HTML code within the context of affected user sessions, exploiting the insufficient input validation and output sanitization processes that govern user-provided data.
The technical implementation of this vulnerability stems from inadequate parameter validation within the avatar handling functionality of ExpressionEngine's core system. When the system processes the avatar parameter through the index.php endpoint, it fails to properly sanitize or escape user-supplied input before rendering it within web pages. This omission creates an exploitable condition where malicious actors can craft specially formatted avatar parameters containing embedded script code that executes in the browsers of unsuspecting users who view affected pages. The vulnerability operates under CWE-79 which specifically addresses cross-site scripting flaws, and aligns with ATT&CK technique T1566.001 for initial access through malicious web content.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the capability to perform session hijacking, data theft, and further escalation within compromised user contexts. An attacker could inject scripts that steal cookies, redirect users to malicious sites, or manipulate the application's functionality to gain unauthorized access to user accounts. The vulnerability's remote nature means that exploitation can occur without requiring local system access or authentication, making it particularly dangerous for web applications hosting user-generated content or managing sensitive data. Users who interact with affected ExpressionEngine installations become potential victims of persistent XSS attacks that can compromise their browsing sessions and personal information.
Mitigation strategies for CVE-2009-1070 should prioritize immediate patching of affected ExpressionEngine versions to the latest available releases that contain proper input validation and output sanitization measures. Organizations should implement comprehensive input validation protocols that filter and sanitize all user-provided parameters including avatar data before processing. Web application firewalls can provide additional protection layers by detecting and blocking malicious payloads attempting to exploit XSS vulnerabilities. Regular security audits and penetration testing should verify that all input handling mechanisms properly escape special characters and validate data formats. The implementation of Content Security Policy headers can further limit the execution scope of injected scripts, while proper output encoding ensures that any malicious content is rendered harmless when displayed to users. Security monitoring should include detection of suspicious avatar parameter patterns and automated scanning for similar vulnerabilities across the web application stack.