CVE-2016-1938 in Firefox
Summary
by MITRE
The s_mp_div function in lib/freebl/mpi/mpi.c in Mozilla Network Security Services (NSS) before 3.21, as used in Mozilla Firefox before 44.0, improperly divides numbers, which might make it easier for remote attackers to defeat cryptographic protection mechanisms by leveraging use of the (1) mp_div or (2) mp_exptmod function.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/06/2022
The vulnerability identified as CVE-2016-1938 resides within the Mozilla Network Security Services (NSS) cryptographic library, specifically in the s_mp_div function located in lib/freebl/mpi/mpi.c. This flaw affects NSS versions prior to 3.21 and is particularly impactful for Mozilla Firefox versions before 44.0. The vulnerability stems from improper handling of number division operations within the multiple precision integer arithmetic implementation, creating a critical weakness in the cryptographic protection mechanisms that rely on these mathematical operations.
The technical flaw manifests in the s_mp_div function which is responsible for performing division operations on multiple precision integers. When this function processes certain inputs, it fails to properly handle edge cases or specific mathematical conditions that should result in deterministic cryptographic behavior. This improper division handling can lead to situations where the cryptographic algorithms that depend on mp_div or mp_exptmod functions produce incorrect results. The vulnerability specifically impacts the mathematical operations used in cryptographic protocols that require precise division and modular exponentiation, potentially allowing attackers to manipulate the outcomes of these critical operations.
The operational impact of this vulnerability is significant as it creates opportunities for remote attackers to compromise cryptographic protection mechanisms. Attackers can leverage this flaw to potentially bypass security controls that rely on proper mathematical operations within the cryptographic library. The vulnerability's exploitation could enable unauthorized access to encrypted communications, compromise digital signatures, or weaken the overall security posture of systems using affected versions of NSS. The specific functions mp_div and mp_exptmod are particularly vulnerable because they form the foundation for many cryptographic algorithms including RSA and Diffie-Hellman key exchanges, making this weakness particularly dangerous in the context of secure communications.
This vulnerability aligns with CWE-191, which addresses integer underflow conditions, and represents a specific case where improper handling of mathematical operations creates security weaknesses in cryptographic implementations. The attack surface is expanded through the use of the ATT&CK technique T1059.001 for command and control operations that might leverage compromised cryptographic functions. The vulnerability demonstrates the critical importance of proper mathematical precision in cryptographic implementations, as even subtle flaws in basic arithmetic operations can have cascading effects on security protocols. Organizations using affected versions of NSS should prioritize immediate patching to address this vulnerability and prevent potential exploitation that could lead to complete compromise of cryptographic protections.
The remediation strategy involves updating to NSS version 3.21 or later, which includes proper fixes for the division handling in the s_mp_div function. Security administrators should also conduct comprehensive testing to ensure that the updated library functions correctly within their specific environments. Additionally, monitoring for potential exploitation attempts and implementing network-based intrusion detection systems can provide additional layers of protection while patches are deployed. The vulnerability serves as a reminder of the critical need for rigorous testing and validation of cryptographic libraries, particularly in environments where security is paramount and the consequences of cryptographic failures can be severe.