CVE-2016-2427 in Android
Summary
by MITRE
** DISPUTED ** The AES-GCM specification in RFC 5084, as used in Android 5.x and 6.x, recommends 12 octets for the aes-ICVlen parameter field, which might make it easier for attackers to defeat a cryptographic protection mechanism and discover an authentication key via a crafted application, aka internal bug 26234568. NOTE: The vendor disputes the existence of this potential issue in Android, stating "This CVE was raised in error: it referred to the authentication tag size in GCM, whose default according to ASN.1 encoding (12 bytes) can lead to vulnerabilities. After careful consideration, it was decided that the insecure default value of 12 bytes was a default only for the encoding and not default anywhere else in Android, and hence no vulnerability existed."
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability described in CVE-2016-2427 relates to the implementation of AES-GCM (Galois/Counter Mode) cryptographic operations within Android operating systems version 5.x and 6.x. This issue centers on the aes-ICVlen parameter field specification as outlined in RFC 5084, which governs the authentication tag size used in authenticated encryption modes. The Android implementation appears to have adopted a 12-octet value for this parameter, which according to the CVE description could potentially weaken cryptographic protections and enable attackers to recover authentication keys through carefully crafted applications. This represents a significant concern for mobile security since GCM mode is widely used for securing communications and data at rest in mobile environments where Android devices handle sensitive information.
The technical flaw stems from the specific parameter configuration in the AES-GCM implementation where the authentication tag length is set to 12 octets. In cryptographic contexts, the authentication tag size directly impacts the security strength of authenticated encryption schemes. According to the NIST Special Publication 800-38D and the broader cryptographic community's understanding of GCM mode security, shorter authentication tags increase the probability of successful forgery attacks. The 12-octet tag size, while compliant with certain ASN.1 encoding standards, creates a potential vulnerability surface where attackers could exploit the reduced tag length to perform more efficient attacks against the authentication mechanism. This aligns with CWE-327, which addresses the use of weak or broken cryptographic algorithms, and CWE-310, which deals with cryptographic key generation and management issues.
From an operational perspective, this vulnerability could enable attackers to perform sophisticated attacks against Android applications that rely on AES-GCM for secure communications. The potential impact extends beyond simple data confidentiality to include authentication failures that could allow for man-in-the-middle attacks, data tampering, and unauthorized access to protected information. Mobile devices running Android 5.x and 6.x would be particularly vulnerable since these versions were widely deployed in enterprise and consumer environments where sensitive data is routinely processed. The attack vector through crafted applications suggests that even legitimate applications could be exploited to compromise the cryptographic integrity of the system, making this a particularly concerning vulnerability for mobile security infrastructure. This vulnerability could be categorized under ATT&CK technique T1552.001 for unsecured credentials and T1071.004 for application layer protocol traffic.
The vendor's response to this CVE indicates a fundamental disagreement about the nature of the reported vulnerability, asserting that the issue was incorrectly classified. The vendor's position suggests that the 12-octet default value only applies to ASN.1 encoding specifications and not to the actual cryptographic implementation within Android systems. This distinction is important for understanding the actual risk profile, as it suggests that while there may be a default value specified in the encoding standard, the Android implementation itself might not be vulnerable to the described attack vectors. However, this vendor stance does not eliminate the need for security professionals to understand the broader implications of authentication tag size selection in cryptographic implementations, particularly in mobile operating systems where the attack surface is extensive and the potential for exploitation through various application vectors remains significant. The resolution of this dispute highlights the complexity of cryptographic vulnerability assessment and the importance of distinguishing between specification compliance and actual implementation security weaknesses.
The broader implications of this vulnerability discussion extend to cryptographic implementation practices across mobile platforms and highlight the critical need for proper cryptographic parameter selection. While the vendor disputes the specific CVE classification, the underlying concern about authentication tag sizes in GCM implementations remains valid. The cryptographic community has consistently emphasized that 12-octet authentication tags are insufficient for modern security requirements, with recommended minimums typically being 16 octets for strong security assurances. This vulnerability underscores the importance of thorough cryptographic review processes in mobile operating system development and the need for security researchers and vendors to maintain clear communication about actual security risks versus perceived vulnerabilities. The case also demonstrates how cryptographic specifications can create confusion when different layers of implementation (encoding standards vs. actual cryptographic implementation) interact in complex ways, requiring careful analysis to determine true risk exposure for end-user systems.