CVE-2025-53945: apko Privilege Escalation Vulnerability

CVE-2025-53945 Overview

CVE-2025-53945 is an Insecure Permissions vulnerability affecting apko, a tool that allows users to build and publish OCI container images built from apk packages. Starting in version 0.27.0 and prior to version 0.29.5, critical files—specifically /etc/ld.so.cache—were inadvertently set to world-writable permissions (0666), which could be abused for local privilege escalation to root.

Critical Impact

Container images built with affected apko versions contain world-writable critical system files, enabling local attackers to escalate privileges to root within the container environment.

Affected Products

• apko versions 0.27.0 through 0.29.4
• OCI container images built with affected apko versions
• Chainguard container infrastructure using vulnerable apko builds

Discovery Timeline

• July 18, 2025 - CVE-2025-53945 published to NVD
• July 22, 2025 - Last updated in NVD database

Technical Details for CVE-2025-53945

Vulnerability Analysis

This vulnerability stems from an improper file permission assignment during the container image build process. When apko generates the /etc/ld.so.cache file—a critical system file used by the dynamic linker (ld.so) to resolve shared library paths—it was being created with overly permissive file mode 0666 (read/write for all users). This insecure permission setting allows any user within the container to modify this file.

The /etc/ld.so.cache file is particularly sensitive because the dynamic linker consults it when loading shared libraries for executable programs. An attacker with the ability to write to this file can inject malicious library paths, causing legitimate programs—including those running as root—to load attacker-controlled shared libraries instead of legitimate system libraries.

Root Cause

The root cause is classified as CWE-276 (Incorrect Default Permissions). During the implementation of the /etc/ld.so.cache generation feature introduced in version 0.27.0, the code failed to explicitly set restrictive file permissions after creating the cache file. The file was created with default permissions that were too permissive for a security-critical system file.

Attack Vector

The attack requires local access to a container built with an affected apko version. An attacker with low-privilege access to the container can:

1. Identify the world-writable /etc/ld.so.cache file
2. Modify the cache to point to attacker-controlled shared library paths
3. Wait for or trigger execution of a privileged process that loads shared libraries
4. Achieve code execution in the context of the privileged process

The security fix properly sets file permissions to 0644 (read/write for owner, read-only for others):

	if err := cacheFile.Write(lsc); err != nil {
		return fmt.Errorf("writing /etc/ld.so.cache: %w", err)
	}
	if err := fsys.Chmod("etc/ld.so.cache", 0644); err != nil {
		return fmt.Errorf("chmod /etc/ld.so.cache: %w", err)
	}

	return nil
}

Source: GitHub Commit aedb077

Detection Methods for CVE-2025-53945

Indicators of Compromise

• Container images with /etc/ld.so.cache having permissions other than 0644
• Unexpected modifications to /etc/ld.so.cache content or timestamps
• Presence of non-standard library paths in the dynamic linker cache
• Anomalous shared library loading behavior in container processes

Detection Strategies

• Scan container images built with apko versions 0.27.0 through 0.29.4 for insecure file permissions
• Implement file integrity monitoring on critical system files including /etc/ld.so.cache
• Use container scanning tools to identify images with world-writable sensitive files
• Audit apko version in CI/CD pipelines and container build infrastructure

Monitoring Recommendations

• Monitor for unauthorized write attempts to /etc/ld.so.cache within containers
• Alert on file permission changes to critical dynamic linker files
• Track shared library loading patterns for anomalous behavior
• Implement runtime security monitoring for privilege escalation attempts

How to Mitigate CVE-2025-53945

Immediate Actions Required

• Upgrade apko to version 0.29.5 or later immediately
• Rebuild all container images that were built with affected apko versions (0.27.0 through 0.29.4)
• Scan deployed containers for world-writable /etc/ld.so.cache files
• Review container security policies to detect insecure file permissions

Patch Information

The vulnerability has been patched in apko version 0.29.5. The fix explicitly sets the correct file permissions (0644) for /etc/ld.so.cache after generation. Users should upgrade to this version or later and rebuild affected container images. For detailed patch information, see the GitHub Security Advisory GHSA-x6ph-r535-3vjw and the v0.29.5 release.

Workarounds

• Manually fix file permissions in container images by adding a chmod step after build
• Use container image scanning to prevent deployment of affected images
• Apply runtime security policies that block writes to /etc/ld.so.cache
• Consider using read-only root filesystems in production containers

# Configuration example
# Check for insecure permissions on existing container images
docker run --rm <image> stat -c '%a %n' /etc/ld.so.cache

# Fix permissions in a running container (temporary workaround)
chmod 644 /etc/ld.so.cache

# Verify apko version before building
apko version
# Ensure version is 0.29.5 or later

# Rebuild container images with patched apko
apko build image.yaml image:latest