CVE-2016-7056 in macOS
Summary
by MITRE
A timing attack flaw was found in OpenSSL 1.0.1u and before that could allow a malicious user with local access to recover ECDSA P-256 private keys.
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Analysis
by VulDB Data Team • 11/20/2022
The vulnerability identified as CVE-2016-7056 represents a critical timing attack flaw in OpenSSL versions 1.0.1u and earlier, specifically affecting the elliptic curve digital signature algorithm implementation. This weakness stems from inconsistent execution times during cryptographic operations, creating observable timing variations that can be exploited by attackers to reconstruct private keys. The flaw exists within the ECDSA signing process where the implementation does not provide constant-time execution for all operations, allowing malicious users with local access to perform statistical analysis on timing measurements.
The technical implementation of this vulnerability resides in the OpenSSL cryptographic library's handling of elliptic curve operations, particularly when processing ECDSA signatures for P-256 curves. The timing variations occur during the scalar multiplication and modular arithmetic operations inherent in ECDSA calculations, where certain operations complete faster or slower depending on the input values. This non-constant time execution creates measurable differences in processing duration that can be captured through repeated measurements. The vulnerability is classified as a timing side-channel attack, which is categorized under CWE-385 and aligns with ATT&CK technique T1059.001 for execution through local access.
The operational impact of CVE-2016-7056 is significant for systems relying on OpenSSL for secure communications, particularly those using ECDSA certificates for authentication and digital signatures. An attacker with local access to a system running vulnerable OpenSSL versions can exploit this flaw to recover private keys used for ECDSA signatures, potentially compromising the entire security infrastructure that depends on these keys. The attack requires minimal privileges and can be executed by any user with local access to the target system, making it particularly dangerous in multi-tenant environments or shared hosting scenarios. The recovery of private keys enables attackers to forge digital signatures, impersonate legitimate entities, and potentially decrypt sensitive communications that were protected using the compromised keys.
Mitigation of this vulnerability requires immediate upgrading of OpenSSL installations to version 1.0.2h or later, which includes proper constant-time implementations for elliptic curve operations. Organizations should also implement comprehensive monitoring to detect potential timing attack attempts and consider deploying additional security controls such as hardware security modules or cryptographic processors that provide protection against side-channel attacks. The fix addresses the core timing variations in the cryptographic implementation and ensures that all operations take constant time regardless of input values. System administrators should conduct thorough vulnerability assessments to identify all systems running vulnerable OpenSSL versions and ensure proper patching across the entire infrastructure. Additionally, organizations should review their key management practices and consider rotating keys that may have been compromised during the vulnerable period, as the attack does not require network access or complex exploitation techniques.