CVE-2018-16132 in Open Whisper Signal App
Summary
by MITRE
The image rendering component (createGenericPreview) of the Open Whisper Signal app through 2.29.0 for iOS fails to check for unreasonably large images before manipulating received images. This allows for a large image sent to a user to exhaust all available memory when the image is displayed, resulting in a forced restart of the device.
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Analysis
by VulDB Data Team • 03/19/2020
The vulnerability identified as CVE-2018-16132 resides within the Open Whisper Signal application version 2.29.0 for iOS devices, specifically affecting the image rendering component known as createGenericPreview. This flaw represents a classic memory exhaustion attack vector that exploits improper input validation within the application's image processing pipeline. The vulnerability stems from the application's failure to implement adequate size checks before attempting to render received images, creating a scenario where malicious or malformed image data can be processed without proper resource constraints.
The technical implementation of this vulnerability involves the createGenericPreview function which handles the generation of image previews for received media content. When a user receives an image through the Signal messaging platform, the application attempts to create a thumbnail or preview version of that image for display purposes. However, the function lacks proper bounds checking to verify whether the incoming image dimensions or file size fall within reasonable parameters. This absence of validation allows attackers to craft specially designed images with extremely large dimensions or compressed data that can cause memory allocation failures during the rendering process.
From an operational perspective, this vulnerability presents a significant risk to Signal users as it can be exploited through simple message transmission without requiring any special privileges or complex attack vectors. The impact manifests as a denial of service condition where the device becomes unresponsive due to memory exhaustion, forcing an automatic restart of the iOS device. This creates a persistent disruption to communication services and can be particularly problematic for users who rely on Signal for critical communications. The vulnerability affects all versions up to 2.29.0, indicating a prolonged window of exposure that could have allowed for widespread exploitation.
The root cause of this vulnerability aligns with CWE-122, which describes improper restriction of operations within a memory buffer, and more specifically relates to CWE-400, which covers the lack of resource limit checks in applications. From an adversary perspective, this vulnerability maps to ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion. The attack requires minimal sophistication as it only requires sending a specially crafted image file, making it particularly dangerous for mass deployment scenarios. The vulnerability demonstrates poor defensive programming practices where input validation should have been implemented at the boundary of image processing operations to prevent uncontrolled memory consumption.
Mitigation strategies should focus on implementing strict size validation for incoming image data before any processing occurs. The application should enforce maximum dimension limits and file size thresholds for images received through the messaging platform. Additionally, proper memory management practices including the use of safe memory allocation functions and implementing timeout mechanisms for image processing operations would help prevent the exploitation of this vulnerability. Regular security audits of image processing components and implementation of automated testing for resource exhaustion scenarios should be incorporated into the development lifecycle. The fix for this vulnerability required updating the createGenericPreview function to include comprehensive input validation and resource management controls to prevent the allocation of excessive memory during image rendering operations.