CVE-2025-57853: Web Terminal Privilege Escalation Flaw

CVE-2025-57853 Overview

A container privilege escalation flaw was discovered in certain Web Terminal images. This vulnerability stems from improper file permissions where the /etc/passwd file is created with group-writable permissions during the container build process. Under specific 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 exploitation path allows the attacker to add a new user with any arbitrary UID, including UID 0, ultimately leading to full root privileges within the container.

Critical Impact

Local attackers with command execution capabilities in affected containers can escalate to root privileges by manipulating the group-writable /etc/passwd file, potentially compromising the entire container environment.

Affected Products

• Web Terminal container images with group-writable /etc/passwd permissions
• Container deployments where non-root users are members of the root group
• Affected container builds created with insecure file permission defaults

Discovery Timeline

• 2026-04-08 - CVE-2025-57853 published to NVD
• 2026-04-08 - Last updated in NVD database

Technical Details for CVE-2025-57853

Vulnerability Analysis

This vulnerability is classified under CWE-276 (Incorrect Default Permissions), a common weakness where software sets insecure permissions during installation or configuration. In this case, the container build process creates the /etc/passwd file with permissions that allow group write access. When a non-root user within the container belongs to the root group (GID 0), they inherit the ability to modify this critical system file.

The attack requires local access to execute commands within the container and depends on the user being a member of the root group. While these conditions narrow the attack surface, containerized environments often run applications with users that are members of the root group for various operational reasons, making this vulnerability relevant in many deployment scenarios.

Root Cause

The root cause is the creation of /etc/passwd with group-writable permissions (e.g., 0664 or similar) during the container image build process. In Linux systems, the /etc/passwd file should typically have permissions of 0644 (owner read/write, group and others read-only). The group-writable permission allows any user who is a member of the file's group (in this case, the root group) to modify its contents.

Attack Vector

The attack requires local access to the container with command execution capabilities. An attacker who has gained a foothold in the container—through legitimate access, a compromised application, or another vulnerability—can check their group membership and the permissions on /etc/passwd. If they are a member of the root group and the file is group-writable, they can append a new user entry with UID 0 to the file, then use su to switch to that user and gain root privileges within the container.

The attack chain typically involves:

1. Verifying group membership using the id command
2. Checking /etc/passwd permissions with ls -la /etc/passwd
3. Appending a new root-level user entry to the file
4. Switching to the newly created user with su

Detection Methods for CVE-2025-57853

Indicators of Compromise

• Unexpected modifications to /etc/passwd within container filesystems
• New user accounts with UID 0 that were not part of the original image
• Unusual su or user-switching activity within container logs
• Changes to file permissions on critical system files

Detection Strategies

• Monitor container runtime for file modification events on /etc/passwd
• Implement file integrity monitoring (FIM) on critical system files within containers
• Review container image build processes for proper permission handling
• Audit running containers for users with root group membership who should not have it

Monitoring Recommendations

• Enable audit logging for file modifications in container environments
• Set up alerts for any write operations to /etc/passwd in production containers
• Monitor for privilege escalation patterns such as su usage following file modifications
• Implement container-aware security monitoring through SentinelOne Singularity Cloud Workload Security

How to Mitigate CVE-2025-57853

Immediate Actions Required

• Audit all Web Terminal container images for group-writable /etc/passwd files
• Rebuild affected container images with correct file permissions (chmod 644 /etc/passwd)
• Review user group assignments within containers to minimize root group membership
• Implement runtime security controls to detect and prevent /etc/passwd modifications

Patch Information

Refer to the Red Hat CVE-2025-57853 Advisory for official guidance and patch availability. Additional technical details can be found in Red Hat Bug Report #2391106. Organizations should update to patched container images as they become available from their respective vendors.

Workarounds

• Manually fix permissions in running containers: chmod 644 /etc/passwd
• Remove unnecessary users from the root group within container images
• Implement read-only root filesystems where possible to prevent runtime modifications
• Use container security policies to block writes to sensitive system files
• Consider using immutable container configurations with security-hardened base images

# Configuration example
# Fix /etc/passwd permissions in Dockerfile
RUN chmod 644 /etc/passwd

# Verify correct permissions in running container
ls -la /etc/passwd
# Expected output: -rw-r--r-- 1 root root ... /etc/passwd

# Check for users with root group membership
getent group root