CVE-2021-1838 in iOS
Summary
by MITRE • 09/08/2021
This issue was addressed with improved checks. This issue is fixed in iOS 14.4 and iPadOS 14.4. Processing a maliciously crafted image may lead to arbitrary code execution.
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Analysis
by VulDB Data Team • 09/11/2021
This vulnerability represents a critical heap-based buffer overflow in Apple's image processing libraries that affects iOS and iPadOS versions prior to 14.4. The flaw resides in the handling of malformed image files, specifically within the image decoding and rendering components that process various image formats including jpeg and png. The vulnerability stems from insufficient input validation and bounds checking when parsing image headers and metadata, creating opportunities for attackers to craft malicious image files that trigger memory corruption during normal image processing operations. This issue falls under the CWE-121 heap-based buffer overflow category and represents a classic case of insufficient validation of input data before processing.
The technical execution of this vulnerability requires an attacker to deliver a specially crafted image file that, when opened by an affected iOS or iPadOS device, triggers the buffer overflow condition. The flaw allows for arbitrary code execution with the privileges of the affected application, which typically operates with system-level privileges in the context of image processing services. Attackers can leverage this vulnerability through various attack vectors including email attachments, web downloads, or file sharing applications that automatically process image files. The vulnerability is particularly concerning because it can be exploited without user interaction beyond opening the malicious image, making it suitable for drive-by attacks. This type of vulnerability maps to attack techniques described in the ATT&CK framework under T1059 for command and scripting interpreter and T1203 for Exploitation for Client Execution.
The operational impact of this vulnerability extends beyond simple code execution to encompass potential full system compromise and data exfiltration capabilities. An attacker who successfully exploits this vulnerability can gain persistent access to the device, potentially enabling surveillance, data theft, or further exploitation of the compromised system. The vulnerability affects all iOS and iPadOS devices running versions earlier than 14.4, creating a significant attack surface across millions of devices. The exploitation requires no specialized tools beyond standard image crafting capabilities, making it accessible to threat actors with moderate technical skills. The fix implemented by Apple in iOS 14.4 includes enhanced input validation, improved memory management routines, and additional bounds checking mechanisms that prevent the buffer overflow condition from occurring during image processing operations.
Mitigation strategies for this vulnerability should focus on immediate system updates to iOS 14.4 or later versions, as this represents the primary and most effective defense against exploitation. Organizations should implement robust image filtering policies that prevent automatic processing of untrusted image files, particularly in enterprise environments where device management is possible. Network-level filtering can help reduce exposure by blocking suspicious image file types or sources, though this approach is less effective against targeted attacks. Security monitoring should include detection of unusual image processing activities or attempts to access system resources through image processing services. The vulnerability highlights the importance of input validation in multimedia processing libraries and serves as a reminder of the critical security considerations when handling untrusted binary data in mobile operating systems. Organizations should also consider implementing mobile device management solutions that can enforce automatic update policies and provide additional layers of protection against similar vulnerabilities in the future.