CVE-2018-10846 in GnuTLS
Summary
by MITRE
A cache-based side channel in GnuTLS implementation that leads to plain text recovery in cross-VM attack setting was found. An attacker could use a combination of "Just in Time" Prime+probe attack in combination with Lucky-13 attack to recover plain text using crafted packets.
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Analysis
by VulDB Data Team • 05/04/2023
The vulnerability identified as CVE-2018-10846 represents a significant cache-based side channel attack against the GnuTLS cryptographic library implementation. This weakness specifically affects the TLS/SSL protocol handling within GnuTLS, creating a pathway for attackers to recover plaintext data through sophisticated cache timing attacks. The vulnerability exploits the fundamental interaction between cryptographic operations and cache behavior in modern processors, particularly when multiple virtual machines share the same physical hardware resources. The attack vector becomes particularly dangerous in cloud computing environments where cross-VM attacks are feasible, as demonstrated by the specific attack methodology that leverages both Just in Time Prime+probe and Lucky-13 techniques. This combination allows adversaries to extract sensitive information from encrypted communications by analyzing cache access patterns and timing variations.
The technical flaw stems from improper handling of cryptographic operations within GnuTLS that create predictable cache access patterns during encryption and decryption processes. When processing TLS packets, the library's implementation does not adequately randomize or mask cache access sequences, making it susceptible to timing-based analysis. The "Just in Time" Prime+probe attack methodology targets specific cache lines that are accessed during cryptographic computations, while the Lucky-13 attack component exploits timing variations in the padding validation process. This dual approach enables attackers to correlate cache behavior with the actual plaintext content, effectively breaking the confidentiality guarantees provided by the TLS protocol. The vulnerability specifically impacts the cipher suite implementations that use certain block cipher modes and padding schemes where the timing differences become exploitable through cache monitoring.
The operational impact of this vulnerability extends beyond simple data leakage, as it fundamentally undermines the security assumptions of encrypted communications in virtualized environments. In cross-VM attack scenarios, an attacker positioned on a different virtual machine sharing the same physical hardware can monitor cache behavior and reconstruct plaintext data from TLS traffic. This creates serious implications for cloud service providers, where multiple customers share underlying infrastructure, and for any environment where virtualization is used to isolate security domains. The vulnerability affects not just the confidentiality of communications but also the integrity of the cryptographic protocol implementation itself, as it demonstrates that even well-established cryptographic libraries can be compromised through side channel attacks. Organizations using GnuTLS for secure communications face potential exposure to sensitive data breaches, including financial information, personal identifiers, and proprietary business data.
Mitigation strategies for CVE-2018-10846 require both immediate patching and architectural considerations to address the underlying cache timing vulnerabilities. The most direct solution involves updating to GnuTLS versions that implement proper cache randomization and timing masking techniques to prevent predictable cache access patterns during cryptographic operations. Security teams should also consider implementing additional layers of protection such as cache isolation mechanisms and virtualization-level mitigations that prevent cross-VM cache monitoring. From a compliance perspective, this vulnerability aligns with CWE-310, which addresses cryptographic weaknesses related to side channel attacks, and maps to ATT&CK technique T1005 for data from local system. Organizations should conduct thorough security assessments of their virtualized environments to identify potential attack vectors and implement proper monitoring for cache-based side channel activities. The vulnerability also highlights the importance of considering physical security implications in virtualized environments, as it demonstrates how hardware-level security features can be exploited to compromise software-level cryptographic protections.