CVE-2023-39320 in Google
Summary
by MITRE • 09/08/2023
The go.mod toolchain directive, introduced in Go 1.21, can be leveraged to execute scripts and binaries relative to the root of the module when the "go" command was executed within the module. This applies to modules downloaded using the "go" command from the module proxy, as well as modules downloaded directly using VCS software.
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Analysis
by VulDB Data Team • 10/02/2023
The vulnerability identified as CVE-2023-39320 represents a critical security flaw in the Go programming language toolchain that emerged with the introduction of the toolchain directive in Go 1.21. This vulnerability specifically targets the go.mod file processing mechanism and creates an execution path that allows malicious actors to run arbitrary scripts and binaries within the context of a Go module. The issue manifests when the go command is executed within a module directory, particularly affecting modules that are downloaded through the module proxy or directly via version control systems. The root cause lies in how the toolchain directive processes module dependencies and executes commands relative to the module root, creating an attack surface that can be exploited by adversaries who gain control over module dependencies.
The technical implementation of this vulnerability stems from the improper handling of the toolchain directive within the go.mod file when modules are fetched and processed. When a module contains a toolchain directive that specifies a toolchain version, the Go toolchain can execute scripts and binaries located in the module's root directory without proper validation of their origin or integrity. This behavior occurs during normal module operations such as go build, go mod download, or go run commands, making the attack surface particularly broad and difficult to detect. The vulnerability is exacerbated by the fact that modules can be downloaded from various sources including public proxies and private repositories, each potentially containing malicious toolchain directives that exploit this execution path. The flaw essentially allows for privilege escalation within the context of the module's directory, enabling attackers to execute arbitrary code with the permissions of the user running the go command.
The operational impact of CVE-2023-39320 is significant across multiple domains of software development and deployment environments. Development teams using Go 1.21 or later versions are at risk when working with modules that contain malicious toolchain directives, potentially compromising entire development environments and build systems. The vulnerability affects not only individual developers but also continuous integration pipelines, containerized deployments, and automated build processes that rely on Go modules. Attackers can leverage this vulnerability to execute malicious code during routine module operations, potentially leading to data exfiltration, system compromise, or further lateral movement within networks. The attack vector is particularly concerning because it can be triggered automatically during normal development workflows, making detection and prevention challenging. This vulnerability aligns with CWE-78 and CWE-74 standards related to command injection and improper input validation, and maps to ATT&CK techniques such as T1059.001 for command and script injection, and T1566 for spearphishing attachments that could contain malicious go.mod files.
Mitigation strategies for CVE-2023-39320 should focus on immediate version updates and operational security measures to prevent exploitation. Organizations should prioritize upgrading to Go versions that address this vulnerability, as newer releases contain patches that properly validate toolchain directives and prevent arbitrary code execution. Additionally, implementing strict module source verification and using trusted module proxies can significantly reduce risk exposure. Security teams should establish monitoring procedures to detect suspicious go.mod files and toolchain directives within development environments. Regular security scanning of module dependencies and implementing software supply chain security practices can help identify potentially malicious modules before they are executed. Organizations should also consider implementing network segmentation and access controls around development environments to limit the potential impact of successful exploitation. The remediation process should include comprehensive code review procedures for all go.mod files, particularly those in critical or external dependencies, and establish security policies that govern module usage and verification processes within development workflows.