CVE-2013-3955 in iOS
Summary
by MITRE
The get_xattrinfo function in the XNU kernel in Apple iOS 5.x and 6.x through 6.1.3 on iPad devices does not properly validate the header of an AppleDouble file, which might allow local users to cause a denial of service (memory corruption) or have unspecified other impact via an invalid file on an msdosfs filesystem.
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Analysis
by VulDB Data Team • 05/25/2021
The vulnerability identified as CVE-2013-3955 resides within the XNU kernel implementation on Apple iOS devices, specifically affecting versions 5.x through 6.1.3 on iPad models. This flaw manifests in the get_xattrinfo function which handles extended attribute information retrieval for filesystem operations. The core issue stems from insufficient validation of AppleDouble file headers during filesystem processing, creating a potential pathway for malicious exploitation. AppleDouble files represent a specific format used to store extended attributes on filesystems that do not natively support them, particularly common in msdosfs implementations where such metadata needs to be preserved across different operating systems.
The technical exploitation of this vulnerability occurs when the kernel processes an AppleDouble file with malformed or invalid header structures on an msdosfs filesystem. The get_xattrinfo function fails to properly validate the integrity and structure of these headers before proceeding with memory operations. This inadequate validation allows an attacker to craft specially formatted AppleDouble files that can trigger memory corruption within the kernel space. The vulnerability represents a classic case of improper input validation where the system assumes the header data conforms to expected formats without sufficient verification mechanisms. The flaw exists at the intersection of filesystem handling and kernel memory management, where unvalidated data structures can lead to unpredictable behavior and system instability.
Operationally, this vulnerability presents a significant risk to iOS device security and reliability. Local users can potentially cause system-wide denial of service conditions through memory corruption, leading to unexpected device crashes or reboots that disrupt normal device operation. The unspecified nature of additional impacts suggests that beyond immediate denial of service, there may be potential for more severe consequences including privilege escalation or information disclosure. The msdosfs filesystem context indicates that this vulnerability affects devices that mount or interact with FAT-formatted storage media, which are common in enterprise and consumer environments where cross-platform file sharing occurs. The exploitation requires local access to the device, making it a privilege escalation vector that could be leveraged by malicious applications or compromised user accounts.
Mitigation strategies for this vulnerability should focus on both immediate patching and operational security measures. Apple released iOS updates addressing this specific issue, and device administrators should ensure all affected systems receive the appropriate security patches. System administrators should also implement monitoring for suspicious filesystem activities on msdosfs volumes and consider restricting user access to potentially vulnerable filesystem operations. The vulnerability aligns with CWE-129, which addresses improper validation of input data, and represents a typical example of how filesystem handling can create kernel-level security risks. From an ATT&CK framework perspective, this vulnerability could be categorized under privilege escalation techniques, specifically targeting kernel memory corruption to gain system-level control. Organizations should also consider implementing filesystem integrity checks and monitoring for unauthorized AppleDouble file creation or modification on affected devices.