CVE-2016-3959 in Google
Summary
by MITRE
The Verify function in crypto/dsa/dsa.go in Go before 1.5.4 and 1.6.x before 1.6.1 does not properly check parameters passed to the big integer library, which might allow remote attackers to cause a denial of service (infinite loop) via a crafted public key to a program that uses HTTPS client certificates or SSH server libraries.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-3959 represents a critical flaw in the Go programming language's cryptographic implementation, specifically within the digital signature algorithm dsa.go file. This issue affects versions prior to 1.5.4 and 1.6.1, creating a potential denial of service condition that can be exploited remotely through carefully crafted public keys. The vulnerability stems from insufficient parameter validation within the Verify function, which processes digital signatures using the Digital Signature Algorithm. When malformed parameters are passed to the underlying big integer library, the system can become trapped in an infinite loop, consuming excessive computational resources and rendering the affected application unavailable to legitimate users.
The technical root cause of this vulnerability lies in the improper handling of input validation within the cryptographic verification process. The Verify function fails to adequately sanitize or validate the parameters provided to the big integer arithmetic library, which is responsible for performing the mathematical operations required for signature verification. This weakness creates a condition where maliciously constructed public key parameters can trigger unexpected behavior in the underlying mathematical libraries, specifically causing arithmetic operations to enter infinite loops. The vulnerability manifests when the cryptographic library attempts to process values that, while syntactically valid, contain characteristics that cause the internal algorithms to cycle indefinitely. This behavior represents a classic example of a resource exhaustion attack vector that can be leveraged to disrupt service availability without requiring authentication or privileged access.
The operational impact of CVE-2016-3959 extends beyond simple denial of service, as it affects critical infrastructure components that rely on Go's cryptographic libraries. Systems utilizing HTTPS client certificate validation or SSH server implementations become vulnerable to this attack, potentially compromising entire networks or services that depend on these protocols for secure communication. The vulnerability is particularly concerning because it can be exploited through legitimate network traffic, making it difficult to detect and mitigate. Attackers can craft specific public key materials that, when processed by vulnerable applications, trigger the infinite loop condition, causing system resources to be consumed rapidly. This creates a scenario where a single malicious connection attempt can render an entire service unavailable, affecting availability and potentially leading to cascading failures in dependent systems. The vulnerability affects both client and server implementations, making it a widespread concern across various networked applications that utilize Go's crypto libraries.
Mitigation strategies for CVE-2016-3959 primarily focus on upgrading to patched versions of the Go programming language, specifically versions 1.5.4 and 1.6.1 or later. Organizations should prioritize immediate patching of all affected systems, particularly those handling HTTPS client certificates or SSH server operations. Additionally, implementing network-level monitoring and intrusion detection systems can help identify suspicious traffic patterns that may indicate exploitation attempts. The vulnerability aligns with CWE-691, which describes insufficient control flow management, and can be categorized under ATT&CK technique T1499.1 for network denial of service. Organizations should also consider implementing input validation controls at application layers and establishing robust monitoring protocols to detect anomalous resource consumption patterns. Security teams should conduct comprehensive vulnerability assessments to identify all systems running affected Go versions and ensure that proper patch management procedures are in place to prevent similar issues from occurring in the future.