CVE-2013-4576 in GnuPG
Summary
by MITRE
GnuPG 1.x before 1.4.16 generates RSA keys using sequences of introductions with certain patterns that introduce a side channel, which allows physically proximate attackers to extract RSA keys via a chosen-ciphertext attack and acoustic cryptanalysis during decryption. NOTE: applications are not typically expected to protect themselves from acoustic side-channel attacks, since this is arguably the responsibility of the physical device. Accordingly, issues of this type would not normally receive a CVE identifier. However, for this issue, the developer has specified a security policy in which GnuPG should offer side-channel resistance, and developer-specified security-policy violations are within the scope of CVE.
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Analysis
by VulDB Data Team • 06/04/2021
The vulnerability described in CVE-2013-4576 represents a significant cryptographic weakness in GnuPG versions 1.x prior to 1.4.16 that stems from improper implementation of RSA key generation processes. This flaw specifically affects the random number generation sequences used during key creation, where certain predictable patterns emerge that create exploitable side channels. The vulnerability operates at the intersection of cryptographic implementation security and physical side-channel attacks, creating a scenario where an attacker with physical proximity can exploit the system's acoustic emissions to reconstruct RSA private keys.
The technical mechanism behind this vulnerability involves the generation of RSA keys through sequences that exhibit specific patterns in their introduction phases, which inadvertently leak information through acoustic side channels. During the decryption process, attackers can perform chosen-ciphertext attacks by analyzing the acoustic signatures produced by the cryptographic operations. The implementation fails to provide adequate side-channel resistance, which is a critical requirement for cryptographic systems according to industry standards such as those outlined in CWE-310. This weakness specifically manifests in the cryptographic library's inability to mask the computational patterns that occur during key generation and decryption operations, making the system susceptible to acoustic cryptanalysis techniques that have been well-documented in the cybersecurity community.
The operational impact of this vulnerability extends beyond simple cryptographic compromise, as it allows physically proximate attackers to extract private keys without requiring sophisticated laboratory equipment or extensive computational resources. The attack vector leverages the natural acoustic emissions from computer hardware during cryptographic operations, making it particularly concerning for environments where physical security controls may be inadequate. This vulnerability directly violates security policies established by the GnuPG development team, who explicitly specified that their software should provide side-channel resistance as part of their security framework. The implications are severe because RSA key compromise can lead to complete system infiltration, as private keys are essential for decrypting communications and authenticating users within GnuPG-based systems.
Mitigation strategies for this vulnerability require immediate upgrade to GnuPG version 1.4.16 or later, which implements proper side-channel resistance measures. Organizations should also consider implementing additional physical security controls to prevent acoustic side-channel attacks, such as soundproofing measures or restricted access to systems performing cryptographic operations. The fix addresses the root cause by ensuring that random number sequences used in key generation do not exhibit predictable patterns that could be exploited through acoustic analysis. This remediation aligns with ATT&CK framework techniques related to credential access and defense evasion, as it prevents attackers from obtaining cryptographic credentials through side-channel methods. Security policies should be updated to reflect the importance of side-channel resistance in cryptographic implementations, particularly for systems handling sensitive information where physical security boundaries may not be sufficient to prevent exploitation.