CVE-2015-8804 in Nettle
Summary
by MITRE
x86_64/ecc-384-modp.asm in Nettle before 3.2 does not properly handle carry propagation and produces incorrect output in its implementation of the P-384 NIST elliptic curve, which allows attackers to have unspecified impact via unknown vectors.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2015-8804 affects the Nettle cryptographic library version 3.1 and earlier, specifically within the x86_64/ecc-384-modp.asm assembly implementation file. This flaw resides in the elliptic curve cryptography implementation for the P-384 NIST elliptic curve, which is a critical component of many security protocols including TLS, SSH, and digital signature systems. The issue stems from improper carry propagation handling during modular arithmetic operations, which are fundamental to elliptic curve point multiplication and scalar multiplication operations that form the backbone of elliptic curve cryptography.
The technical flaw manifests in the assembly code responsible for performing modular arithmetic operations required for elliptic curve computations. When processing large integers in the P-384 curve's finite field arithmetic, the implementation fails to correctly manage carry bits that propagate between word boundaries during multiplication and addition operations. This incorrect carry handling results in corrupted intermediate values that ultimately produce incorrect cryptographic outputs. The vulnerability is particularly dangerous because it affects the core mathematical operations that underpin elliptic curve security, meaning that any cryptographic operations relying on this implementation could produce invalid or predictable results.
The operational impact of this vulnerability is severe and potentially far-reaching across multiple security domains. Attackers could exploit this flaw to manipulate cryptographic operations in ways that compromise the security of systems using affected Nettle versions. The unspecified impact allows for various attack vectors including but not limited to signature forgery, key recovery attacks, and potential decryption of protected communications. The vulnerability affects any system that utilizes Nettle's elliptic curve implementation for P-384 curves, which includes numerous cryptographic libraries, SSL/TLS implementations, and security protocols that depend on this standard curve for authentication and encryption. This represents a critical weakness in the cryptographic infrastructure since elliptic curve cryptography is widely deployed in web security, VPNs, and digital signature systems.
The vulnerability aligns with CWE-681, which addresses incorrect use of a numerical operator, specifically in this case the improper handling of arithmetic operations and carry propagation in cryptographic implementations. From an ATT&CK perspective, this vulnerability could be leveraged as part of a broader attack chain targeting cryptographic systems, potentially enabling techniques such as credential access through signature manipulation or privilege escalation via compromised authentication mechanisms. Organizations using affected systems should immediately update to Nettle version 3.2 or later where this carry propagation issue has been resolved through proper assembly implementation that correctly handles all arithmetic operations. Additionally, system administrators should conduct comprehensive audits of cryptographic libraries and dependencies to ensure no other vulnerable components exist in their security infrastructure, as this type of low-level arithmetic error can have cascading effects on the overall cryptographic security posture of affected systems.