CVE-2023-39323 - Exploiting Line Directives to Bypass Compiler Restrictions and Execute Arbitrary Code in Go

The Go programming language, featured for its simplicity and efficiency in creating modern software, has a newly discovered vulnerability with a Common Vulnerabilities and Exposures (CVE) identifier of CVE-2023-39323. This vulnerability involves using line directives (also known as "//line" comments) to bypass restrictions imposed on "//go:cgo_" directives during the compilation process. By leveraging this technique, an attacker may be able to introduce arbitrary code execution while building a Go application. This post provides an overview of this vulnerability and demonstrates a simple proof of concept showcasing its potential impact.

Background

The Go language uses "//go:cgo_" directives to configure the build environment, which is necessary when working with Cgo (the C interfacing tool for Go). However, some linker and compiler options are blocked due to their risks associated with arbitrary code execution. The CVE-2023-39323 vulnerability revolves around bypassing these restrictions and introducing such blocked flags during the compilation process.

The exploitation of this vulnerability relies on the fact that the "//line" directive (used for providing a different file and line number for the code that follows it) requires the absolute path of the file it refers. Using an absolute path allows an attacker to craft a "//line" directive that manipulates the parser into allowing dangerous flags, leading to arbitrary code execution.

Example

To understand this vulnerability better, let's go through a simple proof of concept. Consider the following code snippet:

package main

import "C"

//line /unsafe:absolute/path/to/your/go/file.go:1
//go:cgo_ldflag "-lblabla"

func main() {
    println("Hello CVE-2023-39323!")
}

The Go parser would typically prevent the use of the unsafe "-lblabla" flag during the build process. However, the use of the "//line" directive with an absolute path effectively bypasses this restriction. When building this program with the command go build, the unsafe flag will be used in the linker, allowing arbitrary code execution.

Exploit Details

Exploiting this vulnerability requires some extra steps compared to other types of attacks. The attacker must know or guess the absolute path of the target Go file, which may not always be easy to determine. However, if successful in obtaining this data, the attacker could craft a malicious "//line" directive that leverages the CVE-2023-39323 vulnerability and potentially introduce unexpected and dangerous behavior during application build.

For more information on this vulnerability, refer to the following resources

1. Go Programming Language Documentation - Provides an overview of the Go language, including features, syntax, and usage.
2. Cgo Documentation - Offers detailed information regarding Cgo, a tool for interfacing Go with C code.
3. CVE-2023-39323 Original Advisory - The official CVE description and classification details for this vulnerability.

Conclusion

CVE-2023-39323 highlights an under-the-hood vulnerability in the Go programming language that potentially allows an attacker to bypass compiler restrictions and introduce arbitrary code execution. While exploiting this issue may be challenging due to absolute path requirements, it still poses a significant risk to developers working with Go and should be carefully considered when using "//line" directives in Go code.

Timeline

Published on: 10/05/2023 21:15:11 UTC
Last modified on: 11/25/2023 11:15:17 UTC