Kaniko is a tool designed to build container images from Dockerfiles within containerized or Kubernetes environments. Versions from 1.25.4 up to but not including 1.25.10 contain a path traversal vulnerability (CWE-22) identified as CVE-2026-28406. The vulnerability arises because kaniko unpacks build context archives by concatenating the destination directory path with the cleaned file name from the archive using filepath.Join(dest, cleanedName), but it does not verify that the resulting path remains inside the intended extraction root. Maliciously crafted tar archives can include entries with relative paths such as '../outside.txt', which escape the extraction directory and write files to arbitrary locations on the host filesystem. This can lead to unauthorized file writes outside the container build context. In scenarios where kaniko is used with registry authentication and docker credential helpers, attackers can chain this path traversal to execute arbitrary code within the kaniko executor process, potentially compromising the build environment. The issue was addressed in version 1.25.10 by switching to securejoin for path resolution during tar extraction, which enforces that extracted files remain within the designated directory. Although no active exploits have been reported, the vulnerability's nature and ease of exploitation make it a critical concern for organizations relying on kaniko for container image builds, especially in automated CI/CD pipelines and multi-tenant Kubernetes clusters.

The vulnerability allows attackers to write files outside the intended extraction directory during container image builds, potentially overwriting critical files or planting malicious payloads. This can compromise the integrity of the build environment and lead to arbitrary code execution, particularly when combined with docker credential helpers in authenticated registry environments. Organizations using kaniko in automated build pipelines or Kubernetes clusters risk unauthorized access, persistent compromise, and lateral movement within their infrastructure. The impact extends to the integrity of container images produced, potentially leading to supply chain attacks if malicious code is embedded during the build process. Availability impact is low but could arise if critical system files are overwritten. Confidentiality impact is minimal directly but can escalate if code execution leads to data breaches. The vulnerability's ease of exploitation without authentication and no user interaction required increases its risk profile significantly.

Upgrade kaniko to version 1.25.10 or later, which includes the fix using securejoin for safe path resolution during tar extraction. Until upgrading is possible, implement strict validation and sanitization of build context archives to ensure no path traversal entries exist before processing. Restrict kaniko execution privileges using container security best practices such as running with least privilege, read-only file systems, and user namespaces to limit the impact of potential exploitation. Monitor build logs and filesystem changes during image builds for unexpected file writes outside the build context. Employ network segmentation and access controls to limit kaniko's ability to interact with credential helpers or sensitive host resources. Regularly audit and rotate credentials used in registry authentication to reduce the risk of credential theft if exploitation occurs. Consider using alternative container build tools with verified secure extraction mechanisms if immediate patching is not feasible.