CVE-2009-3012 in Firefox
Summary
by MITRE
Mozilla Firefox 3.0.13 and earlier, 3.5, 3.6 a1 pre, and 3.7 a1 pre does not properly block data: URIs in Location headers in HTTP responses, which allows remote attackers to conduct cross-site scripting (XSS) attacks via vectors related to (1) injecting a Location header that contains JavaScript sequences in a data:text/html URI or (2) entering a data:text/html URI with JavaScript sequences when specifying the content of a Location header. NOTE: the JavaScript executes outside of the context of the HTTP site.
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Analysis
by VulDB Data Team • 07/05/2018
The vulnerability described in CVE-2009-3012 represents a critical cross-site scripting flaw in Mozilla Firefox versions up to 3.0.13, 3.5, 3.6 a1 pre, and 3.7 a1 pre. This security issue stems from Firefox's improper handling of data: URIs within Location headers of HTTP responses, creating a dangerous bypass mechanism that allows malicious actors to inject and execute arbitrary JavaScript code outside the normal security context of the originating website. The flaw specifically targets the browser's URI processing logic where it fails to adequately sanitize or block data: URIs that contain HTML content with embedded JavaScript sequences, effectively undermining the same-origin policy that protects web applications from cross-site scripting attacks.
The technical implementation of this vulnerability occurs when an attacker crafts a malicious HTTP response containing a Location header with a data:text/html URI that includes JavaScript code. This can be achieved through two primary vectors: either by directly injecting a malicious Location header that contains JavaScript sequences within a data:text/html URI, or by manipulating the content of a Location header to reference a data:text/html URI that contains JavaScript sequences. The browser's failure to properly validate these URIs allows the JavaScript code to execute in an unrestricted context, bypassing the normal security boundaries that should protect users from malicious scripts. This behavior creates a dangerous scenario where malicious code can run with the privileges and access levels of the victim's browser session, potentially leading to complete compromise of the user's browsing environment.
The operational impact of this vulnerability is severe and far-reaching, as it enables attackers to perform sophisticated cross-site scripting attacks that can steal session cookies, credentials, or other sensitive information from users. The fact that the JavaScript executes outside the context of the HTTP site means that traditional security measures such as content security policies and same-origin restrictions become ineffective against this specific attack vector. Attackers can leverage this vulnerability to create convincing phishing attacks, inject malicious code into legitimate websites, or perform session hijacking operations that would otherwise be blocked by standard browser security mechanisms. The vulnerability particularly affects users of older Firefox versions where the security patch had not yet been implemented, leaving them exposed to persistent threats that could compromise their browsing sessions and personal data.
Mitigation strategies for this vulnerability require immediate patching of affected Firefox versions to ensure that the browser properly validates and blocks data: URIs within Location headers. Security administrators should also implement network-level controls such as web application firewalls that can detect and block suspicious Location headers containing data: URIs. Organizations should consider deploying content security policies that explicitly block data: URIs from being executed in HTTP response headers, and users should be educated about the risks of visiting untrusted websites that may serve malicious HTTP responses. The vulnerability aligns with CWE-79 (Cross-site Scripting) and represents a specific implementation flaw in URI handling that maps to ATT&CK technique T1059.007 (Command and Scripting Interpreter: JavaScript), demonstrating how improper input validation can create persistent security weaknesses that allow attackers to bypass fundamental browser security models and execute arbitrary code in user sessions.