CVE-2020-12403 in Network Security Services
Summary
by MITRE • 05/28/2021
A flaw was found in the way CHACHA20-POLY1305 was implemented in NSS in versions before 3.55. When using multi-part Chacha20, it could cause out-of-bounds reads. This issue was fixed by explicitly disabling multi-part ChaCha20 (which was not functioning correctly) and strictly enforcing tag length. The highest threat from this vulnerability is to confidentiality and system availability.
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Analysis
by VulDB Data Team • 06/03/2021
The vulnerability identified as CVE-2020-12403 represents a critical implementation flaw in the Network Security Services (NSS) cryptographic library, specifically affecting the CHACHA20-POLY1305 authenticated encryption algorithm. This issue manifests in NSS versions prior to 3.55 where the CHACHA20-POLY1305 implementation contains a buffer overflow condition that occurs during multi-part ChaCha20 operations. The flaw stems from improper handling of memory boundaries when processing large data sets through multiple processing steps, creating opportunities for attackers to read data from memory locations beyond the intended buffer limits. The vulnerability is classified under CWE-125 as an out-of-bounds read, which directly impacts the confidentiality of encrypted communications and can potentially expose sensitive cryptographic material or system memory contents. The root cause lies in the improper validation of input parameters and memory management during multi-part encryption operations, where the implementation fails to properly track and validate the boundaries of data being processed across multiple function calls.
The operational impact of this vulnerability extends beyond simple data exposure to encompass system availability and integrity concerns. When attackers exploit this out-of-bounds read condition, they can potentially access arbitrary memory locations, which may contain sensitive information such as encryption keys, session data, or other cryptographic material. The vulnerability affects systems that rely on NSS for secure communications, including web browsers, email clients, and network security appliances that utilize the library for TLS/SSL encryption. The specific nature of the flaw means that any application using NSS with CHACHA20-POLY1305 in multi-part mode could be susceptible to this attack vector, making it particularly dangerous in environments where secure communication is paramount. This vulnerability also aligns with ATT&CK technique T1552.001 for unsecured credentials and T1071.004 for application layer protocol traffic, as it compromises the confidentiality of encrypted communications and could potentially enable further exploitation.
The fix implemented by Mozilla and the NSS team addressed this vulnerability by explicitly disabling multi-part ChaCha20 functionality, which was not functioning correctly and posed security risks. This approach follows the principle of least privilege and defense in depth by removing the problematic feature entirely rather than attempting to patch the underlying implementation. The solution also enforces strict tag length validation, ensuring that cryptographic authentication tags are properly validated and that the implementation adheres to the established standards for CHACHA20-POLY1305. Organizations should immediately update to NSS version 3.55 or later to mitigate this vulnerability, as the disabling of multi-part ChaCha20 operations represents a significant change in behavior that may affect applications relying on this specific functionality. The mitigation strategy aligns with industry best practices for cryptographic library management and demonstrates the importance of proper memory management and input validation in security-critical code. System administrators should also monitor for applications that may be using older versions of NSS or that may be vulnerable due to custom implementations that bypass the patched library components.