CVE-2026-25143: melange RCE Vulnerability via Patch Pipeline

CVE-2026-25143 Overview

CVE-2026-25143 is a command injection vulnerability affecting Melange, a tool that allows users to build apk packages using declarative pipelines. The vulnerability exists in the patch pipeline component (pkg/build/pipelines/patch.yaml), where input-derived values such as series paths, patch filenames, and numeric parameters are embedded into shell scripts without proper quoting or validation. This allows an attacker who can influence patch-related inputs to inject shell metacharacters and execute arbitrary commands with the privileges of the melange build process.

Critical Impact

An attacker can achieve arbitrary command execution on the build host by injecting shell metacharacters through patch-related inputs, potentially compromising the entire build environment and any downstream artifacts.

Affected Products

• Melange versions 0.10.0 to 0.40.2 (versions before 0.40.3)

Discovery Timeline

• 2026-02-04 - CVE CVE-2026-25143 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-25143

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw resides in Melange's built-in patch pipeline, which processes user-controlled inputs when constructing shell commands. The pipeline fails to sanitize or properly quote values derived from patch configurations before embedding them into shell script contexts.

When the melange build or melange license-check operations invoke the patch pipeline, the system constructs shell commands using series paths, patch filenames, and numeric parameters from the build configuration. Because these values are not properly escaped, an attacker can include shell metacharacters that break out of their intended string context and inject arbitrary commands.

Root Cause

The root cause lies in the pkg/build/pipelines/patch.yaml file, which directly interpolates input values into shell command strings without implementing proper input validation or shell escaping. The pipeline trusts that configuration inputs are benign, but in scenarios where build configurations can be influenced by external parties (such as pull request-driven CI systems or build-as-a-service platforms), this trust is misplaced.

The vulnerable code patterns involve string concatenation or template substitution that places user-controlled data directly into shell contexts, enabling command injection through characters like backticks, $(...) command substitutions, semicolons, pipes, and redirections.

Attack Vector

An attacker who can influence melange build configurations can exploit this vulnerability through several attack scenarios:

1. Pull Request-Driven CI: By submitting a malicious pull request that modifies melange configuration files to include shell metacharacters in patch-related fields
2. Build-as-a-Service: Through any service that accepts external build configurations for melange packages
3. Supply Chain Attacks: By compromising upstream configurations that are consumed by downstream melange builds

Exploitation involves crafting patch-related input values that contain shell metacharacters. For example, a malicious patch filename could include backtick-enclosed commands or $(command) substitutions that execute when the patch pipeline processes the configuration.

The vulnerability mechanism involves shell metacharacter injection such as backticks for command substitution, $(...) syntax for command execution, semicolons for command chaining, pipes for output redirection, and redirection operators for file manipulation. For technical implementation details, refer to the GitHub Security Advisory GHSA-rf4g-89h5-crcr.

Detection Methods for CVE-2026-25143

Indicators of Compromise

• Unexpected child processes spawned by melange build operations
• Unusual network connections originating from build environments
• Modifications to build artifacts or system files during build processes
• Anomalous shell command patterns in build logs containing metacharacters

Detection Strategies

• Monitor melange build configurations for suspicious characters in patch-related fields, including backticks, $(, semicolons, and pipe characters
• Implement file integrity monitoring on build systems to detect unauthorized modifications
• Review CI/CD pipeline logs for unusual command execution patterns during patch operations
• Deploy runtime application self-protection (RASP) to detect command injection attempts

Monitoring Recommendations

• Enable detailed logging for all melange build operations and review for anomalous patterns
• Implement configuration validation checks before processing build configurations from untrusted sources
• Monitor build host processes for unexpected command executions during patch pipeline stages
• Set up alerts for builds that modify files outside expected directories

How to Mitigate CVE-2026-25143

Immediate Actions Required

• Upgrade Melange to version 0.40.3 or later immediately
• Audit existing melange configurations for potentially malicious input patterns
• Review recent build logs for signs of exploitation, particularly unusual command executions
• Implement strict input validation for any externally-sourced build configurations

Patch Information

The vulnerability has been patched in Melange version 0.40.3. The fix is available in commit bd132535cd9f57d4bd39d9ead0633598941af030. Organizations should upgrade to this version or later to remediate the vulnerability.

For additional details, refer to the GitHub Security Advisory GHSA-rf4g-89h5-crcr.

Workarounds

• Restrict who can modify melange build configurations, particularly patch-related fields
• Run melange builds in isolated, sandboxed environments with minimal privileges
• Implement pre-build configuration validation that rejects inputs containing shell metacharacters
• Disable automated builds from untrusted sources until the patch can be applied

# Configuration example
# Verify current melange version
melange version

# Upgrade melange to patched version
go install chainguard.dev/melange@v0.40.3

# Alternatively, use container image with patched version
docker pull cgr.dev/chainguard/melange:latest