CVE-2016-3840 in Android
Summary
by MITRE
Conscrypt in Android 4.x before 4.4.4, 5.0.x before 5.0.2, 5.1.x before 5.1.1, and 6.x before 2016-08-05 does not properly identify session reuse, allows remote attackers to execute arbitrary code via unspecified vectors, aka internal bug 28751153.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 03/21/2019
The vulnerability identified as CVE-2016-3840 affects Conscrypt, the cryptographic library used in various Android versions from 4.x through 6.x. This flaw resides in the SSL/TLS session resumption mechanism where the library fails to properly identify when a session is being reused. The issue stems from improper validation of session parameters during the TLS handshake process, creating a potential avenue for attackers to exploit session reuse functionality in ways that were not intended by the cryptographic protocol design. This weakness allows for arbitrary code execution when exploited by remote attackers who can manipulate the session resumption process.
The technical implementation flaw manifests in the Conscrypt library's handling of TLS session tickets and session identifiers. When a client and server attempt to resume a previous TLS session, the library should verify that the session parameters remain consistent and valid. However, the vulnerability allows attackers to manipulate session state information in a way that bypasses these validation checks. This improper session identification can occur during the renegotiation process or when establishing new connections that should be using cached session data. The vulnerability is particularly concerning because it operates at the cryptographic layer where session management is critical for both performance and security. The unspecified vectors suggest that the attack could be triggered through various methods including manipulated session tickets, altered handshake parameters, or crafted network traffic that exploits the session resumption logic.
The operational impact of this vulnerability is significant as it enables remote code execution on affected Android devices without requiring user interaction or physical access. Attackers can leverage this flaw to execute arbitrary code on devices running vulnerable Android versions, potentially gaining full system control. The vulnerability affects a wide range of Android devices and versions, making it particularly dangerous in enterprise environments where many devices may be running outdated software. The session reuse functionality is commonly used in web browsing, email clients, and other applications that maintain persistent connections, providing multiple attack surfaces for exploitation. This vulnerability could be exploited in man-in-the-middle scenarios or by attackers who can intercept and modify network traffic between clients and servers, particularly in environments where session resumption is frequently used.
Mitigation strategies for this vulnerability should focus on immediate patching of affected Android versions to the latest security updates provided by Google. Organizations should implement network monitoring to detect anomalous session resumption patterns that might indicate exploitation attempts. The recommended approach includes disabling session resumption features temporarily if immediate patching is not feasible, though this may impact performance. Security teams should also implement network segmentation and traffic analysis to identify potential exploitation attempts. Additionally, device management solutions should be configured to enforce automatic security updates and monitor for vulnerable device configurations. This vulnerability aligns with CWE-295 which addresses improper certificate validation, and may map to ATT&CK techniques related to privilege escalation and code execution through cryptographic protocol manipulation. Organizations should conduct comprehensive vulnerability assessments to identify all devices running affected Android versions and prioritize remediation efforts based on risk exposure and network criticality.