CVE-2016-0818 in Android
Summary
by MITRE
The caching functionality in the TrustManagerImpl class in TrustManagerImpl.java in Conscrypt in Android 4.x before 4.4.4, 5.x before 5.1.1 LMY49H, and 6.x before 2016-03-01 mishandles the distinction between an intermediate CA and a trusted root CA, which allows man-in-the-middle attackers to spoof servers by leveraging access to an intermediate CA to issue a certificate, aka internal bug 26232830.
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Analysis
by VulDB Data Team • 07/10/2022
The vulnerability described in CVE-2016-0818 represents a critical flaw in the SSL/TLS certificate validation mechanism within Android's Conscrypt library implementation. This issue affects multiple Android versions including 4.x before 4.4.4, 5.x before 5.1.1, and 6.x before the 2016-03-01 security update. The core problem lies in how the TrustManagerImpl class handles certificate validation, specifically its improper handling of the distinction between intermediate certificate authorities and trusted root certificate authorities. This fundamental flaw creates a pathway for man-in-the-middle attacks that can compromise the security of encrypted communications.
The technical implementation of this vulnerability stems from the TrustManagerImpl class's failure to properly differentiate between certificate authorities that are trusted root certificates versus those that are merely intermediate certificate authorities. In a properly functioning certificate validation system, intermediate CAs should only be trusted to sign certificates issued by their parent root CAs, while root CAs should be directly trusted for establishing the chain of trust. However, Conscrypt's implementation incorrectly treats intermediate CAs as if they were trusted root CAs, allowing attackers with access to an intermediate CA certificate to issue fraudulent certificates that would be accepted by the Android system. This behavior violates the fundamental principles of public key infrastructure and certificate chain validation as defined by standards such as x509 and PKI protocols.
The operational impact of this vulnerability is severe and far-reaching, as it enables sophisticated man-in-the-middle attacks that can intercept and potentially modify encrypted communications between Android devices and servers. Attackers with access to an intermediate CA certificate can generate valid SSL/TLS certificates for any domain, allowing them to impersonate legitimate services and capture sensitive data transmitted over HTTPS connections. This vulnerability particularly affects mobile applications that rely on secure communications, including banking applications, email clients, and any service requiring encrypted data transmission. The implications extend beyond individual user privacy to potential corporate security breaches, as the vulnerability affects the underlying security infrastructure of Android devices rather than just specific applications.
The attack vector for this vulnerability follows the typical MITM attack pattern where an attacker with access to an intermediate CA certificate can leverage this access to generate fraudulent certificates that will be accepted by vulnerable Android devices. This represents a critical failure in the certificate validation process that violates the principle of least privilege and proper certificate chain validation as outlined in industry standards. The vulnerability demonstrates a clear weakness in the certificate trust model implementation and highlights the importance of proper certificate authority hierarchy enforcement. Organizations should consider this vulnerability as a critical security concern that requires immediate remediation through system updates, and it aligns with attack techniques documented in the MITRE ATT&CK framework under credential access and defense evasion tactics.
Mitigation strategies for this vulnerability primarily involve applying the relevant security patches released by Google for the affected Android versions. System administrators and device managers should prioritize updating affected Android devices to versions that contain the patched Conscrypt implementation. Additionally, organizations should implement network monitoring solutions to detect potential certificate manipulation attempts and consider deploying additional security layers such as certificate pinning for critical applications. The vulnerability also underscores the importance of proper certificate management practices and the need for organizations to regularly audit their certificate trust relationships to prevent similar issues in other components of their security infrastructure.