CVE-2017-9526 in Libgcrypt
Summary
by MITRE
In Libgcrypt before 1.7.7, an attacker who learns the EdDSA session key (from side-channel observation during the signing process) can easily recover the long-term secret key. 1.7.7 makes a cipher/ecc-eddsa.c change to store this session key in secure memory, to ensure that constant-time point operations are used in the MPI library.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-9526 represents a critical cryptographic weakness in the Libgcrypt library affecting versions prior to 1.7.7. This flaw specifically impacts the EdDSA (Edwards-curve Digital Signature Algorithm) implementation and exposes a significant side-channel attack vector that can lead to complete key recovery. The vulnerability arises from insufficient memory management practices during the cryptographic signing process, creating opportunities for attackers to observe and exploit temporal patterns in memory access that reveal sensitive cryptographic information.
The technical flaw stems from the improper handling of session keys within the EdDSA implementation where the session key is stored in regular memory rather than secure memory locations. During the signing process, this memory allocation pattern creates observable side-channel characteristics that allow attackers to perform sophisticated timing or power analysis attacks. The vulnerability manifests when an attacker can observe the signing operations through side-channel means and extract the session key, which then serves as a stepping stone to recover the long-term secret key. This represents a fundamental failure in implementing proper cryptographic side-channel resistance mechanisms.
The operational impact of this vulnerability extends beyond simple confidentiality breaches to compromise the entire cryptographic security model. Once an attacker successfully recovers the long-term secret key through session key observation, they gain the ability to forge signatures, impersonate legitimate entities, and completely undermine the trust model that EdDSA was designed to protect. The vulnerability affects systems using Libgcrypt for cryptographic operations including secure communications, digital signatures, and authentication protocols that rely on EdDSA. This makes it particularly dangerous in environments where cryptographic security is paramount, such as financial services, government communications, and enterprise security infrastructure.
The fix implemented in Libgcrypt 1.7.7 addresses this vulnerability by modifying the cipher/ecc-eddsa.c file to ensure that session keys are stored in secure memory locations that prevent the side-channel leakage patterns. This change enforces constant-time point operations within the MPI (Multi-Precision Integer) library, eliminating the timing variations that previously allowed attackers to observe memory access patterns. The mitigation strategy aligns with established cryptographic best practices and follows the principles outlined in CWE-310, which addresses cryptographic weakness and improper implementation of cryptographic primitives. This vulnerability also relates to ATT&CK technique T1552.001, which covers unsecured credentials, as the exposure of session keys can lead to broader credential compromise scenarios. Organizations should prioritize upgrading to Libgcrypt 1.7.7 or later versions to ensure proper memory management and constant-time operations that prevent side-channel attacks from compromising cryptographic security. The implementation of secure memory allocation and constant-time algorithms represents a fundamental requirement for modern cryptographic libraries to maintain security against sophisticated side-channel adversaries.