CVE-2017-8932 in Google
Summary
by MITRE
A bug in the standard library ScalarMult implementation of curve P-256 for amd64 architectures in Go before 1.7.6 and 1.8.x before 1.8.2 causes incorrect results to be generated for specific input points. An adaptive attack can be mounted to progressively extract the scalar input to ScalarMult by submitting crafted points and observing failures to the derive correct output. This leads to a full key recovery attack against static ECDH, as used in popular JWT libraries.
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Analysis
by VulDB Data Team • 12/12/2022
The vulnerability identified as CVE-2017-8932 represents a critical flaw in the cryptographic implementation of elliptic curve cryptography within the Go programming language ecosystem. This issue specifically targets the P-256 elliptic curve implementation on amd64 architectures, affecting Go versions prior to 1.7.6 and 1.8.x prior to 1.8.2. The flaw manifests in the standard library's ScalarMult function which is fundamental to elliptic curve operations including key exchange and digital signatures. The vulnerability arises from incorrect mathematical computations when processing specific input points, creating a scenario where the cryptographic operations produce erroneous outputs that can be systematically exploited.
The technical nature of this vulnerability stems from a subtle implementation error in the scalar multiplication algorithm used for elliptic curve point multiplication. When the ScalarMult function processes certain edge case input points, it generates incorrect results due to faulty arithmetic operations in the underlying assembly code optimized for amd64 processors. This mathematical inconsistency creates a predictable pattern in the incorrect outputs that can be leveraged by an attacker through adaptive querying techniques. The vulnerability operates on the principle that by carefully crafting input points and observing the resulting failures in computation, an attacker can gradually reconstruct the scalar value being processed through a process known as adaptive attack methodology.
The operational impact of CVE-2017-8932 extends far beyond the immediate cryptographic implementation, particularly affecting widely deployed security protocols and libraries. The vulnerability enables full key recovery attacks against static ECDH implementations, which are extensively used in JSON Web Token (JWT) libraries and other security frameworks. This means that an attacker who can mount the adaptive attack could potentially extract private keys used for authentication and authorization in web applications, mobile applications, and API security systems. The implications are severe as JWT libraries are fundamental to modern web security architectures, making this vulnerability particularly dangerous in environments where token-based authentication is prevalent. The attack can be executed remotely and does not require privileged access, making it highly exploitable in real-world scenarios.
Mitigation strategies for CVE-2017-8932 primarily involve upgrading to patched versions of the Go programming language where the implementation has been corrected. Organizations should prioritize updating their Go runtime environments to versions 1.7.6 or later 1.8.x releases that contain the necessary fixes for the scalar multiplication algorithm. Additionally, security teams should conduct comprehensive audits of their systems to identify all applications and services that rely on vulnerable Go versions, particularly those using JWT libraries or other ECDH-based authentication mechanisms. The vulnerability aligns with CWE-697, which covers incorrect comparison scenarios, and maps to ATT&CK technique T1552.001 for unsecured credentials, as it enables attackers to extract cryptographic keys that are used for authentication purposes. Organizations should also implement monitoring for anomalous cryptographic operations that might indicate exploitation attempts, and consider implementing additional security layers such as certificate pinning and multi-factor authentication to reduce the attack surface.