CVE-2025-8766: Container Privilege Escalation Vulnerability

CVE-2025-8766 Overview

A container privilege escalation vulnerability has been identified in certain Multi-Cloud Object Gateway Core images. This security flaw stems from the /etc/passwd file being created with group-writable permissions during the container image build process. Under certain conditions, an attacker who can execute commands within an affected container—even as a non-root user—can leverage their membership in the root group to modify the /etc/passwd file. This could allow the attacker to add a new user with any arbitrary UID, including UID 0, leading to full root privileges within the container.

Critical Impact

An attacker with command execution capability inside an affected container can escalate to full root privileges by exploiting insecure file permissions on /etc/passwd, potentially compromising container security boundaries.

Affected Products

• Multi-Cloud Object Gateway Core (certain container images)
• Red Hat container images with misconfigured /etc/passwd permissions

Discovery Timeline

• 2026-03-13 - CVE-2025-8766 published to NVD
• 2026-03-16 - Last updated in NVD database

Technical Details for CVE-2025-8766

Vulnerability Analysis

This vulnerability is classified under CWE-276 (Incorrect Default Permissions), a common misconfiguration issue that can have severe security implications in containerized environments. The root cause lies in the build-time configuration of affected container images, where the /etc/passwd file is inadvertently created with group-writable permissions (typically mode 0664 or similar instead of the secure 0644).

In containerized environments, users are often added to the root group (GID 0) to allow certain operations without full root privileges. However, when combined with group-writable permissions on critical system files like /etc/passwd, this creates a privilege escalation pathway. The local attack vector requires the attacker to already have some level of command execution within the container, though the high privileges required suggest this typically involves an attacker with an established foothold or a compromised application running within the container.

Root Cause

The vulnerability originates from the container image build process where the /etc/passwd file is created or modified with incorrect file permissions. Specifically, the file is set with group-writable permissions, allowing any user who is a member of the root group (GID 0) to modify this critical authentication file. This is a violation of the principle of least privilege and represents a significant deviation from secure container image building practices.

Attack Vector

The attack requires local access to the container environment. An attacker who has gained command execution within an affected container—through application vulnerabilities, compromised credentials, or other means—can exploit this flaw if they are a member of the root group. The exploitation process involves:

1. Identifying that /etc/passwd has group-writable permissions
2. Confirming membership in the root group (GID 0)
3. Appending a new user entry with UID 0 to /etc/passwd
4. Switching to the newly created root user to gain full container privileges

The attack methodology involves checking file permissions on /etc/passwd and verifying group membership. If the attacker is in the root group and the file is group-writable, they can add a new user entry with root privileges (UID 0) and then use su to switch to that user. For detailed technical analysis, refer to the Red Hat CVE-2025-8766 Advisory.

Detection Methods for CVE-2025-8766

Indicators of Compromise

• Unexpected modifications to /etc/passwd file within containers, particularly new user entries with UID 0
• Audit logs showing file write operations to /etc/passwd by non-root processes
• Presence of unauthorized user accounts in container environments
• Evidence of su or sudo commands executed shortly after /etc/passwd modifications

Detection Strategies

• Implement file integrity monitoring (FIM) on critical system files including /etc/passwd, /etc/shadow, and /etc/group within containers
• Deploy runtime security tools that can detect privilege escalation attempts in container environments
• Audit container images for insecure file permissions during CI/CD pipeline stages using tools like trivy, grype, or custom scripts
• Monitor for unusual process execution patterns, particularly su or shell spawning by non-interactive processes

Monitoring Recommendations

• Enable container runtime auditing to track file system modifications on sensitive paths
• Configure alerts for any changes to /etc/passwd that are not part of expected container lifecycle operations
• Implement SentinelOne Singularity for Containers to detect and respond to privilege escalation attempts in real-time
• Review container orchestration logs for anomalous container behavior or unexpected privilege changes

How to Mitigate CVE-2025-8766

Immediate Actions Required

• Audit all Multi-Cloud Object Gateway Core container images for group-writable permissions on /etc/passwd
• Rebuild affected container images with correct file permissions (mode 0644 for /etc/passwd)
• Restrict user membership in the root group (GID 0) to only those processes that absolutely require it
• Implement container security policies that prevent modification of system authentication files

Patch Information

Organizations should consult the Red Hat CVE-2025-8766 Advisory for official guidance on patched container image versions. Additionally, the Red Hat Bug Report #2387265 contains detailed tracking information for this vulnerability. Update to the latest patched container images as they become available from Red Hat.

Workarounds

• Manually fix file permissions in running containers by executing chmod 644 /etc/passwd as a temporary measure (note: this change will not persist across container restarts unless the image is rebuilt)
• Use read-only root filesystems where possible to prevent runtime modification of system files
• Implement Kubernetes PodSecurityPolicies or Pod Security Standards to enforce secure container configurations
• Consider running containers with a non-root user that is not a member of the root group

# Configuration example - Verify and fix /etc/passwd permissions in containers
# Check current permissions
ls -la /etc/passwd

# If group-writable (e.g., -rw-rw-r--), fix permissions
chmod 644 /etc/passwd

# Verify the fix
ls -la /etc/passwd
# Expected output: -rw-r--r-- 1 root root ... /etc/passwd

# For Dockerfile remediation, add this line after any passwd modifications:
# RUN chmod 644 /etc/passwd