CVE-2016-6489 in Nettle
Summary
by MITRE
The RSA and DSA decryption code in Nettle makes it easier for attackers to discover private keys via a cache side channel attack.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2016-6489 resides within the Nettle cryptographic library implementation of RSA and DSA decryption operations. This flaw represents a significant security weakness that directly impacts the confidentiality and integrity of cryptographic operations. The issue stems from the implementation's susceptibility to cache side channel attacks, where an attacker can potentially reconstruct private keys through careful analysis of memory access patterns and cache behavior during cryptographic computations. Such attacks exploit the temporal and spatial locality properties of modern computer architectures to infer sensitive information from seemingly innocuous operations.
The technical root cause of this vulnerability lies in the non-constant time implementation of the decryption algorithms within the Nettle library. During RSA and DSA decryption processes, the cryptographic operations do not execute in a consistent time frame regardless of the input data. This variation in execution time creates observable patterns that can be monitored through cache side channel attacks. The implementation fails to properly mask the timing variations that occur during modular exponentiation and other mathematical operations essential to the decryption process. This vulnerability is categorized under CWE-310 as "Cryptographic Implementation Fault" and specifically relates to timing variations that leak information about the cryptographic key.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally compromises the security model of any system relying on Nettle for cryptographic operations. An attacker with sufficient access to monitor cache behavior and timing information can reconstruct RSA private keys over time through repeated observations of the decryption process. This vulnerability affects systems using Nettle version 2.3 through 3.2, making it particularly concerning given the widespread adoption of this cryptographic library in various open source projects and embedded systems. The attack requires only local access or the ability to monitor cache behavior, making it particularly dangerous in environments where such monitoring capabilities exist.
Mitigation strategies for this vulnerability involve implementing constant-time cryptographic algorithms that do not vary execution time based on input values. The recommended approach includes updating to Nettle version 3.3 or later, where the implementation has been corrected to use constant-time operations throughout the RSA and DSA decryption processes. Organizations should also consider implementing additional protections such as cache flushing mechanisms, randomization of memory access patterns, and hardware-level mitigations where available. This vulnerability aligns with ATT&CK technique T1005 as it involves data from local system storage and T1059 for potential command execution to monitor system behavior. System administrators should prioritize patching affected systems and conducting thorough security assessments to identify any potential exploitation attempts that may have occurred before the fix was applied.