CVE-2015-8803 in Nettle
Summary
by MITRE
The ecc_256_modp function in ecc-256.c in Nettle before 3.2 does not properly handle carry propagation and produces incorrect output in its implementation of the P-256 NIST elliptic curve, which allows attackers to have unspecified impact via unknown vectors, a different vulnerability than CVE-2015-8805.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2015-8803 affects the Nettle cryptographic library version 3.1 and earlier, specifically within the ecc_256_modp function located in ecc-256.c. This flaw represents a critical implementation error in the P-256 NIST elliptic curve arithmetic that fundamentally undermines the security guarantees of elliptic curve cryptography. The issue stems from improper handling of carry propagation during modular arithmetic operations, which is a core component of elliptic curve implementations. When cryptographic operations involving the P-256 curve are performed, the incorrect carry handling leads to mathematically invalid results that compromise the entire cryptographic process. This vulnerability operates at the foundational level of elliptic curve arithmetic, where carry propagation is essential for maintaining numerical accuracy in large integer operations. The flaw falls under CWE-682, which addresses incorrect arithmetic operations, and specifically relates to improper carry handling in cryptographic implementations. The impact extends beyond simple mathematical errors to potentially enable attackers to exploit the flawed implementation in ways that could compromise the security of systems relying on this cryptographic library.
The operational implications of this vulnerability are severe and multifaceted, as it affects the core cryptographic operations that secure communications, digital signatures, and key exchanges in numerous applications. When the ecc_256_modp function fails to properly manage carry propagation, it produces incorrect modular arithmetic results that can lead to invalid elliptic curve points or malformed cryptographic outputs. This incorrect behavior can manifest in various attack vectors that leverage the mathematical inconsistencies to bypass security mechanisms, potentially allowing attackers to forge signatures, decrypt communications, or perform other unauthorized cryptographic operations. The unspecified impact mentioned in the vulnerability description reflects the complexity of how incorrect elliptic curve arithmetic can be exploited, as the exact attack surface depends on how the library is integrated into applications and what cryptographic operations are performed. The vulnerability operates at the intersection of the NIST P-256 curve specification and the implementation details of the Nettle library, creating a scenario where even subtle mathematical errors can have catastrophic security consequences. This type of flaw is particularly dangerous because it affects the mathematical foundation of the cryptographic system rather than just a specific API or interface.
Mitigation strategies for CVE-2015-8803 require immediate updates to the Nettle library to version 3.2 or later, which contains the corrected implementation of the ecc_256_modp function. Organizations should conduct comprehensive inventory assessments to identify all systems and applications that depend on the vulnerable Nettle library, particularly those implementing elliptic curve cryptography for TLS/SSL certificates, digital signatures, or secure communications. System administrators must prioritize patching operations and verify that the updated library properly handles carry propagation in elliptic curve operations. Security teams should implement monitoring for unusual cryptographic behavior or potential exploitation attempts that might indicate an active attack leveraging this vulnerability. The fix addresses the underlying carry propagation issue in the modular arithmetic implementation, ensuring that the P-256 curve operations produce mathematically correct results. Additionally, organizations should consider implementing cryptographic libraries that have undergone extensive security auditing and formal verification processes to reduce the risk of similar implementation flaws. This vulnerability demonstrates the critical importance of thorough mathematical verification in cryptographic implementations and aligns with ATT&CK technique T1552.001, which covers credentials from password storage, as the compromised cryptographic operations can effectively undermine the security of credential protection mechanisms that rely on elliptic curve cryptography. The vulnerability also relates to ATT&CK technique T1499.001, which addresses network denial of service, as incorrect cryptographic operations can lead to system instability or service disruption when the flawed arithmetic produces invalid results that break cryptographic protocols.