CVE-2018-0735 in OpenSSL
Summary
by MITRE
The OpenSSL ECDSA signature algorithm has been shown to be vulnerable to a timing side channel attack. An attacker could use variations in the signing algorithm to recover the private key. Fixed in OpenSSL 1.1.0j (Affected 1.1.0-1.1.0i). Fixed in OpenSSL 1.1.1a (Affected 1.1.1).
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Analysis
by VulDB Data Team • 06/03/2023
The vulnerability identified as CVE-2018-0735 represents a critical timing side channel attack against OpenSSL's implementation of the Elliptic Curve Digital Signature Algorithm. This flaw resides in the cryptographic library's handling of ECDSA signatures where variations in execution time during the signing process can be exploited by malicious actors. The vulnerability specifically affects OpenSSL versions 1.1.0 through 1.1.0i and 1.1.1 versions prior to 1.1.1a, creating a significant risk for systems relying on ECDSA for digital signatures and certificate validation. The timing variations occur due to the implementation's lack of constant-time operations during the signature generation process.
The technical root cause of this vulnerability stems from the non-constant time execution of the ECDSA signing algorithm within OpenSSL's cryptographic implementation. When performing ECDSA signature operations, the algorithm's execution time varies depending on the input data and internal computations, creating measurable timing differences that can be amplified through statistical analysis. This timing leakage occurs primarily during the scalar multiplication operations within the elliptic curve arithmetic, where the implementation does not maintain consistent execution paths regardless of input values. The vulnerability aligns with CWE-388, which classifies issues related to improper handling of timing information and side channel attacks, specifically addressing the lack of constant-time cryptographic implementations that are essential for preventing timing-based information leakage.
The operational impact of this vulnerability extends beyond simple cryptographic weakness to encompass potential system compromise and data integrity breaches. An attacker with sufficient computational resources and access to the signing process can perform repeated timing measurements to reconstruct the private key through statistical analysis and machine learning techniques. This attack vector particularly threatens systems that frequently generate ECDSA signatures, such as certificate authorities, secure communication servers, and any infrastructure relying on ECDSA for authentication and digital signatures. The vulnerability can be exploited in various attack scenarios including man-in-the-middle attacks, certificate forgery, and authentication bypasses, making it a severe concern for organizations maintaining cryptographic security. According to ATT&CK framework, this vulnerability maps to T1552.001, which covers the exploitation of credential access through cryptographic attacks and the manipulation of cryptographic systems.
Mitigation strategies for CVE-2018-0735 require immediate patching of affected OpenSSL versions to the fixed releases including OpenSSL 1.1.0j and 1.1.1a. Organizations should prioritize updating their cryptographic libraries and ensuring that all systems utilizing ECDSA signatures are protected against timing side channel attacks. Additionally, implementing proper monitoring for unusual timing patterns during signature operations can help detect potential exploitation attempts. Security teams should also consider deploying constant-time cryptographic implementations where possible and regularly audit their cryptographic infrastructure for similar vulnerabilities. The fix implemented in OpenSSL addresses the timing variations by ensuring that all cryptographic operations execute in constant time regardless of input values, thereby eliminating the information leakage that previously enabled private key recovery attacks. Organizations should also conduct thorough vulnerability assessments to identify any other cryptographic implementations that may be susceptible to similar timing side channel attacks.