CVE-2021-43568 in ecdsa-elixir
Summary
by MITRE • 11/10/2021
The verify function in the Stark Bank Elixir ECDSA library (ecdsa-elixir) 1.0.0 fails to check that the signature is non-zero, which allows attackers to forge signatures on arbitrary messages.
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Analysis
by VulDB Data Team • 11/12/2021
The vulnerability identified as CVE-2021-43568 resides within the Stark Bank Elixir ECDSA library version 1.0.0, specifically within its verify function implementation. This flaw represents a critical cryptographic weakness that fundamentally undermines the security assurances provided by the elliptic curve digital signature algorithm. The library serves as a cryptographic component for generating and verifying digital signatures in various applications, making this vulnerability particularly concerning for systems relying on secure authentication mechanisms. The issue manifests when the verification process fails to validate that the signature components meet essential mathematical requirements for cryptographic validity.
The technical flaw stems from the absence of a critical validation check within the signature verification routine. In proper ECDSA implementations, signature verification must ensure that both the r and s components of the signature are non-zero values within the appropriate mathematical bounds defined by the elliptic curve parameters. The absence of this validation creates a condition where attackers can craft malformed signatures that pass the verification process despite not being legitimate signatures generated by the private key. This failure directly violates the fundamental principles of digital signature cryptography where verification should rigorously confirm the mathematical relationship between the signature, the message, and the public key.
The operational impact of this vulnerability extends far beyond simple cryptographic weakness, as it enables attackers to perform signature forgery attacks against any system utilizing the affected library. An attacker could potentially forge valid signatures for arbitrary messages, allowing unauthorized access to protected resources, authentication bypass, and manipulation of signed data. This capability undermines the core security properties of authentication, integrity, and non-repudiation that digital signatures are designed to provide. Systems relying on this library for secure communications, transaction validation, or access control mechanisms become vulnerable to sophisticated attacks that exploit this validation gap.
The vulnerability maps directly to CWE-327, which addresses the use of weak cryptographic algorithms, and CWE-330, which covers the use of insufficiently random values in cryptographic contexts. From an attacker perspective, this weakness aligns with techniques described in the MITRE ATT&CK framework under the T1552.001 technique for "Unsecured Credentials" and potentially T1078.004 for "Valid Accounts: Cloud Accounts" when attackers leverage forged signatures to gain unauthorized access. Organizations using this library should immediately implement mitigation strategies including library version updates, additional signature validation layers, and comprehensive security testing to identify systems potentially compromised by this vulnerability. The remediation process requires not only updating to patched versions of the ecdsa-elixir library but also conducting thorough security audits of systems that may have been exposed to forged signatures during the vulnerable period.
This vulnerability demonstrates the critical importance of rigorous cryptographic implementation practices and the necessity of comprehensive validation checks in security-sensitive code. The flaw underscores that even seemingly minor omissions in cryptographic verification routines can lead to complete compromise of security assurances, emphasizing the need for peer review and formal security validation of cryptographic implementations.