CVE-2016-4852 in YoruFukurou
Summary
by MITRE
YoruFukurou (NightOwl) before 2.85 relies on support for emoji skin-tone modifiers even though this support is missing from the CoreText CTFramesetter API on OS X 10.9, which allows remote attackers to cause a denial of service (application crash) via a crafted emoji character sequence.
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Analysis
by VulDB Data Team • 04/16/2019
The vulnerability identified as CVE-2016-4852 affects YoruFukurou version 2.85 and earlier, representing a critical denial of service flaw that exploits the application's handling of emoji skin-tone modifiers. This issue specifically manifests on macOS 10.9 systems where the CoreText CTFramesetter API lacks proper support for emoji skin-tone modifiers, creating a fundamental compatibility gap between the application's expected functionality and the underlying operating system capabilities. The flaw demonstrates how modern application development can inadvertently create security vulnerabilities through assumptions about platform features that may not be universally supported across different operating system versions.
The technical root cause of this vulnerability stems from the application's reliance on emoji skin-tone modifier functionality without proper fallback mechanisms or platform compatibility checks. When YoruFukurou processes crafted emoji character sequences containing skin-tone modifiers, it attempts to utilize CoreText CTFramesetter API functions that are simply unavailable or non-functional on macOS 10.9. This mismatch creates a scenario where the application encounters a fatal error when trying to render or process these specific character sequences, leading to immediate application termination and complete denial of service for end users. The vulnerability operates at the text rendering layer, specifically targeting the composition and display mechanisms within the application's user interface.
From an operational perspective, this vulnerability presents significant risk to users of older macOS versions who may be running the affected YoruFukurou application. Attackers can exploit this flaw by crafting malicious emoji sequences that, when processed by the vulnerable application, trigger application crashes and system instability. The impact extends beyond simple inconvenience to potential disruption of productivity, particularly for users who rely on this messaging application for communication. The vulnerability also highlights the importance of thorough compatibility testing across different operating system versions and the dangers of making assumptions about platform capabilities that may not hold true in all deployment environments.
Security practitioners should note that this vulnerability aligns with CWE-248, which addresses "Uncaught Exception" conditions, and demonstrates how improper error handling can lead to denial of service scenarios. The flaw also relates to ATT&CK technique T1499.004, which involves "Endpoint Denial of Service" through application or system crashes. Organizations should implement immediate mitigations including updating to YoruFukurou version 2.85 or later, which contains the necessary patches to properly handle emoji sequences without relying on unsupported CoreText functionality. Additionally, system administrators should consider implementing application sandboxing or monitoring for unusual crash patterns that might indicate exploitation attempts, while also ensuring that users are aware of the risks associated with processing untrusted emoji content in messaging applications.