CVE-2013-1693 in Firefox
Summary
by MITRE
The SVG filter implementation in Mozilla Firefox before 22.0, Firefox ESR 17.x before 17.0.7, Thunderbird before 17.0.7, and Thunderbird ESR 17.x before 17.0.7 allows remote attackers to read pixel values, and possibly bypass the Same Origin Policy and read text from a different domain, by observing timing differences in execution of filter code.
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Analysis
by VulDB Data Team • 05/17/2021
The vulnerability identified as CVE-2013-1693 represents a sophisticated side-channel attack targeting the SVG filter implementation within Mozilla Firefox and Thunderbird browser applications. This security flaw exists in versions prior to 22.0 for Firefox, 17.0.7 for Firefox ESR, and corresponding versions of Thunderbird and its ESR variants. The vulnerability exploits timing variations in the execution of filter code to extract sensitive information through a technique known as timing-based information leakage. The attack vector specifically targets the rendering engine's handling of SVG filter operations, which are commonly used in web graphics and visual effects.
The technical flaw manifests through the implementation of SVG filters that process pixel data in a manner susceptible to timing analysis attacks. When browsers execute SVG filter operations, particularly those involving complex filtering algorithms, the time required for execution varies based on the underlying pixel values being processed. Attackers can exploit this timing differential by carefully crafting malicious SVG content that triggers specific filter operations and measuring the execution time to infer pixel data or text content from different domains. This represents a violation of the fundamental web security principle that browsers should prevent cross-origin information leakage through various means including timing channels.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks that could bypass critical security mechanisms. The Same Origin Policy, which is fundamental to web security and prevents scripts from accessing resources from different domains, becomes compromised through this timing-based approach. Attackers can potentially extract text content from different domains by observing how filter execution times change when processing different pixel values, effectively creating a covert channel for data exfiltration. This vulnerability particularly affects web applications that rely on secure cross-origin resource sharing and could enable attackers to gather sensitive information from authenticated sessions or protected resources.
The security implications of CVE-2013-1693 align with CWE-203, which specifically addresses "Observable Timing Discrepancy" in software implementations. This vulnerability also maps to ATT&CK technique T1059.001, which covers "Command and Scripting Interpreter: PowerShell" and other execution techniques that leverage timing-based reconnaissance. The attack demonstrates how seemingly benign web features can become security risks when implementation details leak information through timing variations. Organizations using affected browser versions face significant risk as this vulnerability can be exploited through malicious websites without requiring user interaction, making it particularly dangerous for widespread deployment. The remediation process requires updating to patched versions of the affected applications, with Mozilla releasing versions 22.0 and 17.0.7 respectively that address the timing discrepancies in SVG filter execution. Security teams should monitor for exploitation attempts and ensure all affected systems receive immediate updates to prevent potential data breaches through timing-based information leakage attacks.
This vulnerability highlights the importance of considering timing channels in security assessments of web browser implementations and demonstrates how complex rendering features can introduce unexpected security risks. The attack methodology relies on the fundamental principle that execution time variations can reveal information about underlying data, making it a classic example of a side-channel attack that requires careful consideration of all system behaviors. The fix implemented by Mozilla involved modifying the SVG filter execution engine to ensure consistent timing regardless of the pixel values being processed, thereby eliminating the information leakage channel that attackers could exploit.