CVE-2011-4692 in WebKit
Summary
by MITRE
WebKit, as used in Apple Safari 5.1.1 and earlier and Google Chrome 15 and earlier, does not prevent capture of data about the time required for image loading, which makes it easier for remote attackers to determine whether an image exists in the browser cache via crafted JavaScript code, as demonstrated by visipisi.
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Analysis
by VulDB Data Team • 09/14/2025
This vulnerability resides in the WebKit rendering engine used by Apple Safari and Google Chrome browsers, specifically affecting versions up to 5.1.1 and 15 respectively. The flaw represents a timing-based side-channel attack that exploits the difference in load times between cached and non-cached resources. When a browser attempts to load an image that exists in its cache, the loading process completes much faster than when loading a new resource from the network. This temporal discrepancy creates a measurable timing difference that can be leveraged by malicious actors to infer cache state information.
The technical implementation of this vulnerability occurs through JavaScript's ability to measure time intervals between operations. Attackers craft specific JavaScript code that attempts to load images from various URLs and measures the time taken for each load operation. When an image is successfully retrieved from cache, the load time is significantly reduced compared to when the browser must fetch the resource from the network. This timing differential provides attackers with information about whether specific resources exist in the browser's cache, potentially exposing sensitive user data or application state information.
The operational impact of this vulnerability extends beyond simple cache enumeration. While initially demonstrated through the visipisi technique, this timing attack could be used to determine user browsing patterns, track user behavior across sessions, or even infer the existence of specific resources that might be considered sensitive. The vulnerability essentially allows attackers to perform cache-based reconnaissance, potentially leading to more sophisticated attacks that combine this information with other reconnaissance techniques. This type of attack falls under the category of information leakage through timing channels, which is classified as CWE-203 in the Common Weakness Enumeration framework.
From a cybersecurity perspective, this vulnerability demonstrates the challenges inherent in browser security and the complexity of preventing information leakage through seemingly benign features. The attack requires no special privileges or access to the target system, making it particularly dangerous as it can be executed from any web page that the user visits. The technique relies on the fundamental behavior of web browsers to cache resources for performance optimization, which creates an unintended information disclosure channel. This vulnerability aligns with several tactics in the MITRE ATT&CK framework, specifically those related to reconnaissance and information gathering, where adversaries attempt to understand the target environment and identify potential attack vectors through indirect means rather than direct exploitation.
Mitigation strategies for this vulnerability require browser vendors to implement measures that normalize load times regardless of cache state, effectively eliminating the timing differential that attackers exploit. This can be achieved through techniques such as introducing random delays in resource loading, implementing consistent timing mechanisms for cache and network operations, or modifying how browsers report loading completion times to JavaScript. Users should maintain updated browser versions where possible, as this vulnerability was addressed in subsequent releases through improved timing normalization mechanisms. Organizations should also consider implementing content security policies and monitoring for suspicious JavaScript behavior that might indicate attempts to exploit this or similar timing-based vulnerabilities. The vulnerability underscores the importance of considering side-channel attacks during security design reviews and highlights the need for comprehensive security testing that includes timing-based analysis.