CVE-2018-12440 in BoringSSL
Summary
by MITRE
BoringSSL through 2018-06-14 allows a memory-cache side-channel attack on DSA signatures, aka the Return Of the Hidden Number Problem or ROHNP. To discover a DSA key, the attacker needs access to either the local machine or a different virtual machine on the same physical host.
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Analysis
by VulDB Data Team • 02/19/2020
The vulnerability described in CVE-2018-12440 represents a significant side-channel attack against DSA signature implementations within BoringSSL, a cryptographic library widely used in Google's products and services. This weakness stems from the Return Of the Hidden Number Problem (ROHNP) attack vector that exploits memory cache behaviors to recover private DSA keys. The vulnerability specifically affects BoringSSL versions released through June 14, 2018, making it a substantial concern for systems that rely on DSA signatures for cryptographic operations. The attack mechanism leverages the predictable patterns in memory cache access that occur during DSA signature computations, allowing adversaries to infer sensitive key material through statistical analysis of cache behavior.
The technical flaw manifests in how BoringSSL implements DSA signature operations, particularly during modular exponentiation and other cryptographic computations that involve secret key material. When processing DSA signatures, the cryptographic library exhibits cache access patterns that vary based on the bits of the secret key being processed. This cache timing variation creates a leakage channel that can be exploited by attackers who have access to the same physical hardware or virtual environment. The vulnerability is particularly insidious because it requires minimal privileges to exploit - attackers only need access to either the local machine or a co-located virtual machine on the same physical host, making it a serious concern for cloud environments and multi-tenant systems.
The operational impact of this vulnerability extends far beyond simple cryptographic compromise, as DSA key recovery would enable attackers to forge signatures, impersonate legitimate entities, and potentially gain unauthorized access to systems that rely on DSA-based authentication. This attack is especially concerning in cloud computing environments where virtual machines share physical hardware resources, as it demonstrates how side-channel attacks can bridge the isolation boundaries between virtual environments. The vulnerability affects systems using DSA signatures for TLS certificates, code signing, digital signatures, and other security protocols that depend on DSA key material. Organizations with infrastructure running vulnerable BoringSSL versions face potential compromise of their entire cryptographic ecosystem, as the recovered keys could be used to decrypt communications, forge documents, or bypass authentication mechanisms.
Mitigation strategies for this vulnerability require immediate patching of all affected BoringSSL implementations, with particular attention to systems running vulnerable versions released prior to June 14, 2018. Organizations should also consider implementing additional security measures such as cache timing attack mitigations, ensuring proper virtual machine isolation in shared hosting environments, and transitioning away from DSA signatures to more secure alternatives like ECDSA or RSA. The attack model aligns with ATT&CK technique T1059.001 for privilege escalation through local access and T1552.001 for credential access via cryptographic key compromise. This vulnerability is classified under CWE-203, which specifically addresses the exposure of sensitive information through side-channel analysis. System administrators should also consider implementing hardware security modules or trusted execution environments to provide additional protection against such cache-based side-channel attacks.