CVE-2016-3898 in Android
Summary
by MITRE
Telephony in Android 5.0.x before 5.0.2, 5.1.x before 5.1.1, 6.x before 2016-09-01, and 7.0 before 2016-09-01 allows attackers to cause a denial of service (loss of locked-screen 911 TTY functionality) via a crafted application that modifies the TTY mode by broadcasting an intent, aka internal bug 29832693.
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Analysis
by VulDB Data Team • 09/15/2022
This vulnerability affects Android telephony systems across multiple versions including 5.0.x before 5.0.2, 5.1.x before 5.1.1, 6.x before 2016-09-01, and 7.0 before 2016-09-01, specifically targeting the locked-screen 911 TTY functionality. The issue stems from insufficient validation of TTY mode modifications through broadcast intents, allowing malicious applications to manipulate telephony services during emergency situations. This represents a critical security flaw in the Android operating system's telephony subsystem that could potentially compromise emergency response capabilities.
The technical flaw resides in the Android telephony framework's handling of TTY (Teletypewriter) mode changes, where the system fails to properly validate or restrict broadcast intents that modify TTY settings. When a crafted malicious application broadcasts an intent to change TTY mode, the system processes this without adequate authorization checks or input validation. This vulnerability is categorized under CWE-284 Access Control, specifically involving improper access control mechanisms for telephony services. The flaw enables attackers to exploit the telephony subsystem's intent handling mechanism to manipulate emergency communication channels, particularly affecting the locked-screen 911 functionality that relies on TTY mode for accessibility.
The operational impact of this vulnerability is significant as it directly affects emergency response capabilities, particularly for users who rely on TTY services for communication. When the locked-screen 911 TTY functionality is compromised, users cannot access emergency services through the telephony system during screen lock states, potentially leading to life-threatening situations. This vulnerability aligns with ATT&CK technique T1486 Data Encrypted for Impact, as it disrupts the availability of critical emergency services and can be classified as a denial of service attack against telephony functions. The attack vector involves simple intent broadcasting from malicious applications, making it easily exploitable and difficult to detect within the system's normal operation.
Mitigation strategies should focus on implementing proper intent validation and access control mechanisms within the Android telephony framework. System administrators and device manufacturers should ensure that all affected Android versions are updated to the latest security patches that address this vulnerability. The fix typically involves strengthening the validation of broadcast intents that modify TTY modes, implementing proper authorization checks before allowing mode changes, and ensuring that emergency telephony services maintain their availability regardless of application-level modifications. Additionally, users should be advised to avoid installing untrusted applications and to keep their devices updated with the latest security patches. This vulnerability highlights the importance of maintaining robust security controls around emergency services and accessibility features in mobile operating systems, as these components are critical for user safety and system reliability.