CVE-2018-10844 in GnuTLS
Summary
by MITRE
It was found that the GnuTLS implementation of HMAC-SHA-256 was vulnerable to a Lucky thirteen style attack. Remote attackers could use this flaw to conduct distinguishing attacks and plaintext-recovery attacks via statistical analysis of timing data using crafted packets.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/04/2023
The vulnerability identified as CVE-2018-10844 represents a critical weakness in the GnuTLS cryptographic library's implementation of HMAC-SHA-256, a widely used message authentication code algorithm. This flaw falls under the category of timing side-channel attacks, where attackers exploit variations in processing time to infer sensitive information about encrypted communications. The vulnerability specifically affects the cryptographic implementation's resistance to statistical analysis, making it susceptible to attacks that rely on measuring and analyzing timing discrepancies during cryptographic operations.
The technical nature of this vulnerability stems from the improper implementation of the HMAC-SHA-256 algorithm within GnuTLS, which creates predictable timing variations during message authentication code computation. This weakness enables attackers to perform Lucky thirteen style attacks, where they analyze timing data from network packets to distinguish between different ciphertexts and potentially recover plaintext information. The flaw operates at the cryptographic protocol level, affecting TLS implementations that rely on GnuTLS for secure communications. This type of vulnerability is classified under CWE-310 as "Cryptographic Issues" and more specifically relates to CWE-312, "Cleartext Storage of Sensitive Information" in the context of timing data leakage, though the primary concern here is timing side-channel analysis rather than direct cleartext storage.
The operational impact of this vulnerability extends across numerous systems and applications that depend on GnuTLS for secure communications, including web servers, email servers, and various network services. Remote attackers can exploit this weakness without requiring local access or elevated privileges, making it particularly dangerous in networked environments. The attack vector involves sending crafted packets to target systems, where the timing variations in HMAC-SHA-256 processing can be statistically analyzed to infer information about the encrypted data. This vulnerability directly impacts the confidentiality and integrity of communications, as attackers can potentially reconstruct plaintext messages or distinguish between different ciphertexts, undermining the fundamental security properties that cryptographic protocols are designed to provide. The attack requires only network access and does not necessitate complex infrastructure, making it accessible to a wide range of threat actors.
Mitigation strategies for CVE-2018-10844 primarily involve updating to patched versions of GnuTLS where the timing variations in HMAC-SHA-256 implementation have been addressed through constant-time algorithmic implementations. System administrators should prioritize updating their GnuTLS installations and verify that all affected applications using the library have been updated accordingly. Organizations should also implement monitoring for unusual timing patterns in network communications that might indicate exploitation attempts. The fix typically involves ensuring that cryptographic operations take constant time regardless of input values, preventing attackers from inferring information through timing analysis. Security teams should also consider implementing additional network-level protections such as intrusion detection systems that can detect unusual packet timing patterns, and regularly audit cryptographic implementations to ensure compliance with security best practices. This vulnerability highlights the importance of constant-time implementations in cryptographic libraries and the need for thorough security testing of cryptographic operations against side-channel attacks, aligning with ATT&CK techniques such as T1005 for Data from Local System and T1041 for Exfiltration Over C2 Channel, though the primary concern here is the weakening of cryptographic security through timing analysis rather than direct data exfiltration.