CVE-2008-5015 in Firefox
Summary
by MITRE
Mozilla Firefox 3.x before 3.0.4 assigns chrome privileges to a file: URI when it is accessed in the same tab from a chrome or privileged about: page, which makes it easier for user-assisted attackers to execute arbitrary JavaScript with chrome privileges via malicious code in a file that has already been saved on the local system.
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Analysis
by VulDB Data Team • 08/20/2019
This vulnerability resides in the privilege separation mechanisms of Mozilla Firefox versions 3.x prior to 3.0.4, specifically addressing how the browser handles chrome privileges for file system access. The flaw occurs when a user navigates to a file: URI within the same browser tab from a privileged chrome or about: page context. This creates an unexpected privilege escalation scenario where local files that have already been saved to the user's system can be accessed with elevated chrome privileges. The vulnerability exploits the browser's trust model by allowing malicious code embedded in locally stored files to execute with the same privileges as chrome UI components, effectively bypassing the security boundaries that normally protect against local file access attacks.
The technical implementation of this vulnerability stems from Firefox's URI handling logic and privilege assignment system. When a user accesses a file: URI from a privileged context such as chrome:// or about: pages, the browser incorrectly grants chrome privileges to the file URI, even though the file was originally accessed through a non-privileged context. This privilege leak occurs because Firefox fails to properly validate the security context of file URIs when they are accessed in a tab that previously contained privileged content. The flaw represents a classic case of improper privilege management where the browser's security boundaries are not properly enforced across different navigation contexts.
The operational impact of CVE-2008-5015 is significant for user-assisted attacks, as it requires only that a user navigate to a malicious file that has already been saved locally on their system. Attackers can craft malicious JavaScript code within files that have been previously downloaded or saved by the user, then trick the victim into accessing these files through a privileged browsing context. This creates a scenario where attackers can execute arbitrary code with chrome privileges, potentially allowing them to access sensitive browser data, manipulate browser UI components, or perform actions that would normally be restricted to privileged browser processes. The vulnerability essentially allows attackers to escalate their privileges from standard user-level access to chrome-level privileges within the browser environment.
This vulnerability aligns with CWE-284 Access Control flaws, specifically addressing improper privilege management where the system fails to properly enforce access controls between different privilege levels. The flaw also corresponds to ATT&CK technique T1059.007 Command and Scripting Interpreter: JavaScript, as it enables attackers to execute malicious JavaScript code with elevated privileges. Additionally, it relates to T1566.001 Phishing: Spearphishing Attachment, since attackers can deliver malicious files through phishing campaigns and then exploit this vulnerability to gain elevated privileges. The vulnerability demonstrates a critical gap in Firefox's security model where context-based privilege assignment fails to maintain proper security boundaries, making it particularly dangerous in environments where users might be tricked into accessing malicious files.
Mitigation strategies for this vulnerability include updating to Firefox 3.0.4 or later versions where the privilege assignment logic has been corrected to properly validate URI contexts and prevent unauthorized privilege escalation. Organizations should implement security awareness training to prevent users from accessing suspicious files, particularly those that have been downloaded from untrusted sources. Browser hardening measures such as disabling file URI access or implementing strict content security policies can also help reduce the attack surface. Additionally, maintaining up-to-date browser versions and implementing regular security audits of browser configurations will help prevent exploitation of this and similar privilege escalation vulnerabilities. The fix implemented by Mozilla addresses the core issue by ensuring that file: URIs maintain their original privilege level regardless of the browsing context from which they are accessed, thereby preventing the unintended privilege escalation that made this vulnerability exploitable.