CVE-2008-3950 in iPod touch
Summary
by MITRE
Off-by-one error in the _web_drawInRect:withFont:ellipsis:alignment:measureOnly function in WebKit in Safari in Apple iPhone 1.1.4 and 2.0 and iPod touch 1.1.4 and 2.0 allows remote attackers to cause a denial of service (browser crash) via a JavaScript alert call with an argument that lacks breakable characters and has a length that is a multiple of the memory page size, leading to an out-of-bounds read.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability described in CVE-2008-3950 represents a critical off-by-one error within WebKit's text rendering subsystem that specifically affects Apple's Safari browser implementation on iPhone and iPod touch devices. This flaw exists in the _web_drawInRect:withFont:ellipsis:alignment:measureOnly function, which handles the rendering of text within browser windows and manages the display of truncated text using ellipsis characters. The issue manifests when processing JavaScript alert dialogs containing specially crafted string arguments that lack breakable characters and possess lengths that are exact multiples of memory page boundaries, creating a scenario where memory access violations can occur.
The technical root cause of this vulnerability stems from improper boundary checking during text measurement and rendering operations. When the browser encounters a JavaScript alert with an argument that meets the specific criteria of having no breakable characters and a length that aligns with memory page boundaries, the text measurement algorithm fails to properly account for the final character boundary, resulting in an out-of-bounds memory read operation. This type of error falls under CWE-129, which addresses improper validation of array indices, and represents a classic example of how seemingly benign text processing operations can lead to critical system instability when boundary conditions are not properly handled.
The operational impact of this vulnerability is significant as it allows remote attackers to execute a denial of service attack against affected devices without requiring any user interaction beyond visiting a malicious webpage. The attack vector is particularly concerning because it leverages JavaScript alert calls, which are commonly used in web applications and therefore frequently encountered by users. When successfully exploited, the vulnerability causes Safari to crash and restart, effectively denying users access to the browser functionality and potentially disrupting their web browsing experience. This attack model aligns with ATT&CK technique T1499.004, which describes the use of resource exhaustion attacks to cause denial of service conditions.
The exploitation of this vulnerability requires minimal privileges and can be executed through standard web browsing activities, making it particularly dangerous in environments where users may encounter malicious content without proper security measures. The specific requirements for successful exploitation - namely the absence of breakable characters and precise memory page alignment - make this vulnerability somewhat targeted but still highly effective when encountered in the wild. This type of memory corruption vulnerability represents a serious concern for mobile browser security and demonstrates the importance of rigorous input validation and boundary checking in text rendering systems.
Mitigation strategies for this vulnerability include immediate software updates from Apple that address the specific boundary checking issues in the WebKit rendering engine, implementation of web content filtering systems that can detect and block malicious JavaScript patterns, and deployment of network-level security controls that can identify and prevent exploitation attempts. Organizations should prioritize patch management for affected iOS versions and consider implementing additional browser hardening measures to reduce the attack surface. The vulnerability serves as a reminder of the critical importance of memory safety in browser implementations and the need for comprehensive testing of boundary conditions in text processing functions, particularly in mobile environments where resource constraints can exacerbate memory management issues.