CVE-2025-68736 Linux Kernel Landlock Vulnerability – Analysis, Impact & Mitigation

Vulnerability Overview

What is CVE-2025-68736?

CVE-2025-68736 is a high-severity vulnerability in the Linux kernel’s Landlock security module that affects how access rights are evaluated for files accessed through disconnected directories and bind mounts. The vulnerability stems from incomplete mount point consideration during access rights evaluation, potentially allowing sandboxed applications to gain broader permissions than intended.

The Landlock module is a critical security component designed to provide application sandboxing capabilities. When properly configured, it restricts what files and directories applications can access. However, this vulnerability creates a gap in that protection by failing to account for mount point hierarchies when evaluating access rights for disconnected directories.

Why Landlock Security Matters

Landlock provides a lightweight sandboxing mechanism that allows unprivileged users to restrict their own access rights. This is particularly valuable in modern Linux deployments where:

• Container orchestration platforms rely on kernel-level security mechanisms
• Multi-tenant environments require strong isolation between workloads
• Applications need to self-impose restrictions to limit the impact of potential compromises
• Development teams want to enforce principle of least privilege at the kernel level

The module has gained significant adoption in recent years as organizations prioritize defense-in-depth strategies. A vulnerability in Landlock directly undermines these security investments.

Severity Classification and Impact

CVSS Score: High (specific score pending official publication)

Impact Assessment:

• Confidentiality: High – Unauthorized file access through disconnected directories
• Integrity: High – Potential modification of restricted files
• Availability: Low – No direct denial of service mechanism identified

The vulnerability requires local access to exploit, limiting its immediate threat surface. However, in containerized environments or multi-user systems, this represents a significant privilege escalation vector.

Technical Deep Dive

How the Landlock Module Works

Landlock operates by allowing processes to voluntarily restrict their own access rights through a set of rules. These rules define which files and directories a process can access and what operations it can perform. The module evaluates access requests against these rules before allowing filesystem operations.

The access evaluation process typically involves:

1. Intercepting filesystem operation requests
2. Traversing the filesystem hierarchy to locate the target resource
3. Evaluating access rules against the resource’s path
4. Granting or denying the operation based on rule matching

This design provides fine-grained control while maintaining performance through efficient rule evaluation.

The Disconnected Directory Problem

A disconnected directory occurs when a directory is renamed or moved from its original location but remains accessible through a bind mount. This creates a critical mismatch:

Original filesystem hierarchy:
/home/user/data/sensitive/
  └─ file.txt
After rename and bind mount:
/home/user/data/
  └─ file.txt (disconnected from original path)
/mnt/restricted/
  └─ file.txt (bind mount to renamed directory)

In this scenario, the same file is accessible through two different paths with potentially different access control implications. The vulnerability occurs because Landlock’s access evaluation may not properly account for the mount point context when evaluating the disconnected path.

Mount Point Evaluation Failure

The core technical issue involves how the kernel evaluates access rights when a file is accessed through a bind mount pointing to a disconnected directory. The vulnerability manifests when:

1. A Landlock rule restricts access to a specific path (e.g., /home/user/data/)
2. A directory within that path is renamed or moved
3. A bind mount is created pointing to the disconnected directory
4. The process accesses the file through the bind mount path

The kernel fails to properly evaluate whether the bind mount path should inherit the restrictions from the original path, potentially allowing access that should be denied.

Access Rights Widening Mechanism

The vulnerability enables “access rights widening” – a situation where a sandboxed process gains more permissions than its Landlock rules should allow. This occurs through:

• Path confusion: The kernel evaluates access based on the disconnected path rather than the mount point
• Hierarchy mismatch: Access rules tied to the original filesystem hierarchy don’t apply to the bind mount hierarchy
• Incomplete validation: The access evaluation doesn’t verify that the mount point itself complies with the sandboxing rules

Affected Systems

Linux Kernel Versions at Risk

While specific version ranges are still being finalized by the Linux kernel security team, the vulnerability affects:

• Stable kernel series: Versions with Landlock support (5.13 and later)
• Long-term support kernels: All LTS versions with Landlock enabled
• Distribution kernels: Any distribution kernel with Landlock support and the vulnerable code path

Note: Check your distribution’s security advisory for precise version information, as backports and version numbering vary.

Deployment Scenarios Most Vulnerable

Certain deployment patterns face elevated risk:

1. Container Platforms: Kubernetes, Docker, and other container runtimes using Landlock for workload isolation
2. Sandboxed Applications: Applications using Landlock for self-imposed restrictions (browsers, media players, etc.)
3. Multi-tenant Systems: Shared hosting environments relying on Landlock for tenant isolation
4. Development Environments: Systems where developers use Landlock for testing and validation

How to Identify Your Kernel Version

Execute the following command to determine your current kernel version:

uname -r

To check if Landlock is enabled in your kernel:

grep -i landlock /boot/config-$(uname -r)

Output should show CONFIG_SECURITY_LANDLOCK=y if Landlock is enabled.

For detailed kernel configuration information:

cat /proc/config.gz | gunzip | grep LANDLOCK

Attack Scenarios and Exploitation

Unauthorized File Access Through Bind Mounts

Scenario: A containerized application is sandboxed with Landlock rules restricting access to /app/data/. An attacker with local access:

1. Renames /app/data/sensitive/ to /app/data/.hidden/
2. Creates a bind mount: mount --bind /app/data/.hidden/ /tmp/accessible/
3. Accesses files through /tmp/accessible/ which bypass the original Landlock rules
4. Reads sensitive configuration files or credentials

Impact: Confidentiality breach, potential credential exposure

Privilege Escalation in Sandboxed Environments

Scenario: A sandboxed service account with restricted permissions:

1. Exploits the vulnerability to access /etc/shadow or other privileged files
2. Extracts password hashes or other sensitive system information
3. Uses this information to escalate privileges or move laterally

Impact: Privilege escalation, lateral movement capability

Data Integrity Compromise

Scenario: A restricted application gains write access through the vulnerability:

1. Modifies configuration files it shouldn’t access
2. Injects malicious code into application binaries
3. Alters audit logs to cover tracks

Impact: System compromise, audit trail manipulation, supply chain risk

Real-World Attack Chain

1. Initial Compromise
   └─ Attacker gains local access (compromised container, local user account)
2. Reconnaissance
   └─ Identify Landlock-restricted directories
   └─ Map bind mount configuration
3. Exploitation
   └─ Create disconnected directory through rename operations
   └─ Establish bind mount to bypass Landlock rules
   └─ Access restricted files
4. Post-Exploitation
   └─ Extract sensitive data
   └─ Establish persistence
   └─ Escalate privileges
   └─ Move laterally to other systems

Detection and Assessment

Kernel Version Verification

Begin with a systematic inventory of all systems:

#!/bin/bash
# Scan all systems for vulnerable kernel versions
for host in $(cat /path/to/hostlist.txt); do
  echo "Checking $host..."
  ssh $host "uname -r && grep LANDLOCK /boot/config-\$(uname -r)"
done

Document findings in a spreadsheet with columns for:

• Hostname
• Kernel version
• Landlock enabled (yes/no)
• Patch status
• Priority for patching

Monitoring Access Logs for Exploitation Signs

Configure audit rules to detect suspicious access patterns:

# Add to /etc/audit/rules.d/landlock.rules
-w /proc/sys/kernel/landlock/ -p wa -k landlock_changes
-a always,exit -F arch=b64 -S mount -S umount2 -k mount_operations
-a always,exit -F arch=b64 -S rename -S renameat -k file_rename

Monitor for:

• Unusual bind mount operations
• Rapid directory rename sequences
• Access to files through unexpected paths
• Landlock rule modifications

Security Audit Checklist

• [ ] Inventory all systems running Linux with Landlock enabled
• [ ] Identify applications using Landlock for sandboxing
• [ ] Review current Landlock rule configurations
• [ ] Audit bind mount configurations for suspicious patterns
• [ ] Check access logs for exploitation attempts
• [ ] Verify patch availability from your distribution vendor
• [ ] Test patches in non-production environments
• [ ] Document current security posture and baseline metrics

Tools and Commands for Detection

Landlock Status Check:

# Verify Landlock support
cat /sys/kernel/security/landlock/abi_version

Bind Mount Enumeration:

# List all bind mounts
mount | grep bind
findmnt -t bind

Access Log Analysis:

# Search for suspicious file access patterns
ausearch -k mount_operations -ts recent
ausearch -k file_rename -ts recent

Process Landlock Status:

# Check if a process has Landlock restrictions
cat /proc/[PID]/status | grep Landlock

Remediation Strategy

Immediate Kernel Update Procedure

Phase 1: Preparation (Day 1)

1. Verify patch availability from your distribution:

• Red Hat/CentOS: Check Red Hat Security Advisories (RHSA)
• Ubuntu/Debian: Check Ubuntu Security Notices (USN)
• SUSE: Check SUSE Security Updates
• Arch: Check Arch Linux Security Tracker

1. Create a maintenance window schedule
2. Prepare rollback procedures
3. Notify stakeholders of planned maintenance

Phase 2: Testing (Days 2-3)

1. Apply patches to test/staging environments
2. Run comprehensive application testing
3. Verify Landlock functionality remains intact
4. Monitor for performance regressions
5. Validate monitoring and logging systems

Phase 3: Production Deployment (Days 4-7)

For non-critical systems:

# Update kernel package
sudo apt update && sudo apt install linux-image-generic
# or
sudo yum update kernel
# Reboot system
sudo reboot

For critical systems, use rolling updates:

# Update one system at a time
# Monitor for issues before proceeding to next system
# Maintain service availability through load balancing

Phase 4: Verification (Ongoing)

# Verify patched kernel is running
uname -r
# Confirm Landlock is still functional
cat /sys/kernel/security/landlock/abi_version
# Check system logs for errors
journalctl -xe

Access Control Review and Tightening

After patching, conduct a comprehensive access control audit:

1. Review Landlock Rules:

• Document all active Landlock policies
• Verify rules align with principle of least privilege
• Remove overly permissive rules

1. Audit Bind Mount Configuration:

• Identify all bind mounts in /etc/fstab
• Review temporary bind mounts in system logs
• Validate that bind mounts don’t bypass intended restrictions

1. Tighten Restrictions:

• Implement more granular Landlock rules
• Restrict directory rename operations where possible
• Use read-only mounts for sensitive data

Example hardened Landlock configuration:

// Restrict to specific directories only
landlock_add_rule(ruleset, LANDLOCK_RULE_PATH_BENEATH,
    &(struct landlock_path_beneath_attr) {
        .allowed_access = LANDLOCK_ACCESS_FS_READ_FILE,
        .parent_fd = open("/app/data", O_PATH | O_CLOEXEC),
    }, 0);

Monitoring Implementation

Deploy enhanced monitoring post-patch:

# Create comprehensive audit rule set
cat > /etc/audit/rules.d/landlock-enhanced.rules << 'EOF'
# Monitor Landlock-related operations
-w /proc/sys/kernel/landlock/ -p wa -k landlock_config
-a always,exit -F arch=b64 -S mount -S umount2 -F dir=/mnt -k mount_mnt
-a always,exit -F arch=b64 -S rename -S renameat -F dir=/app -k app_rename
-a always,exit -F arch=b64 -S open -F dir=/app/data -F perm=w -k data_write
# Alert on suspicious patterns
-a always,exit -F arch=b64 -S bind -k bind_operations
EOF
# Reload audit rules
sudo service auditd restart

Rollback Considerations

Maintain rollback capability:

1. Kernel Backup:

   # Keep previous kernel available
   # Most distributions maintain multiple kernel versions
   # Verify bootloader can access previous kernel

1. Rollback Procedure:

• Boot into previous kernel from GRUB menu
• Verify system stability
• Investigate root cause of issues
• Re-test patched kernel

1. Rollback Triggers:

• Critical application failures
• Performance degradation >20%
• Landlock functionality loss
• Unexpected security issues

Operational Guidance

Patch Management Timeline

Recommended Timeline for Organizations:

Expedited Timeline for High-Risk Environments:

• Container platforms: Days 1-5
• Multi-tenant systems: Days 1-5
• Systems with sensitive data: Days 1-7

Testing Before Production Deployment

Comprehensive Test Plan:

1. Functional Testing:

• Verify all applications start correctly
• Test normal application workflows
• Validate Landlock restrictions are enforced
• Confirm bind mounts function as expected

1. Security Testing:

• Attempt to exploit CVE-2025-68736 (should fail)
• Verify access controls are enforced
• Test Landlock rule evaluation
• Validate audit logging

1. Performance Testing:

• Measure system performance metrics
• Monitor CPU, memory, and I/O usage
• Compare against baseline
• Identify any regressions

1. Compatibility Testing:

• Test with all supported applications
• Verify third-party integrations
• Check container runtime compatibility
• Validate monitoring tool functionality

Team Communication and Training

Stakeholder Communication:

1. Executive Summary (for leadership):

• What: High-severity Linux kernel vulnerability
• When: Patches available now
• Impact: Potential unauthorized file access
• Action: Kernel updates required within 2 weeks

1. Technical Details (for IT/Security teams):

• Vulnerability mechanism and exploitation
• Affected systems and versions
• Patch testing and deployment procedures
• Monitoring and detection methods

1. User Communication (if applicable):

• Planned maintenance windows
• Expected service impact
• No action required from users
• Contact information for issues

Training Topics:

• Landlock security module overview
• Disconnected directory risks
• Bind mount security implications
• Exploitation detection and response
• Patch management procedures

Documentation Updates

Update organizational documentation:

1. Security Policies:

• Add Landlock configuration standards
• Document bind mount restrictions
• Define access control requirements

1. Runbooks:

• Kernel patching procedures
• Rollback procedures
• Incident response procedures
• Monitoring alert responses

1. Architecture Documentation:

• Update system diagrams with security controls
• Document Landlock rule configurations
• Record bind mount configurations
• Update threat models

1. Incident Response:

• Add CVE-2025-68736 to incident response playbook
• Define escalation procedures
• Document forensic analysis procedures
• Create communication templates

Frequently Asked Questions

What is a disconnected directory and why does it matter?

A disconnected directory is one that has been renamed or moved from its original location but remains accessible via a bind mount. This creates a mismatch between the filesystem hierarchy and the mount point hierarchy.

Why it matters: Landlock rules are typically tied to specific filesystem paths. When a directory becomes disconnected through renaming, the kernel may evaluate access rights based on the disconnected path rather than the mount point path, potentially bypassing intended restrictions.

Example:

Original rule: Allow read access to /app/data/
Directory renamed: /app/data/sensitive/ → /app/data/.hidden/
Bind mount created: /tmp/accessible/ → /app/data/.hidden/
Result: Access through /tmp/accessible/ may bypass the original rule

How does this vulnerability affect sandboxed applications?

Sandboxed applications using Landlock can inherit broader access rights than intended when accessing files through disconnected directories. This undermines the security model by allowing:

• Reading files that should be restricted
• Modifying configuration or data files
• Accessing system files or other applications’ data
• Escalating privileges within the sandbox

The vulnerability is particularly concerning because it affects the kernel-level security mechanism that applications rely on for isolation.

Which Linux distributions are affected?

Any distribution using affected Linux kernel versions with Landlock support is vulnerable. This includes:

• Red Hat/CentOS: RHEL 8.x, 9.x with Landlock-enabled kernels
• Ubuntu: Ubuntu 20.04 LTS and later with Landlock support
• Debian: Debian 11 (Bullseye) and later
• SUSE: SUSE Linux Enterprise 15 SP3 and later
• Arch Linux: Current and recent releases
• Fedora: Fedora 33 and later

Check your specific distribution’s security advisory for precise version information and patch availability.

What should I do if I’m running an affected kernel version?

Follow these steps immediately:

1. Assess: Determine if Landlock is enabled and actively used
2. Prioritize: Identify critical systems requiring urgent patching
3. Test: Apply patches to staging environments first
4. Deploy: Roll out patches to production systems
5. Verify: Confirm patches are applied and systems are functioning
6. Monitor: Implement enhanced monitoring for exploitation attempts
7. Review: Audit access controls and Landlock configurations

Do not delay patching, as the vulnerability can be exploited by local attackers to gain unauthorized access.

Can this vulnerability be exploited remotely?

No. CVE-2025-68736 requires local access to the system to exploit. Remote exploitation is not possible because:

• The attacker must create disconnected directories (requires local filesystem access)
• Bind mount operations require local system access
• The vulnerability is in the kernel’s local access evaluation

However, in containerized environments or multi-user systems, compromised local accounts or containers can leverage this vulnerability to escalate privileges or access other users’ data.

How do I verify if my system has been compromised?

Conduct a forensic investigation:

1. Review Access Logs:

   ausearch -k mount_operations -ts recent
   ausearch -k file_rename -ts recent

1. Check File Integrity:

   # Compare against known-good baseline
   aide --check

1. Audit Bind Mounts:

   mount | grep bind
   findmnt -t bind

1. Review Process Activity:

   # Check for suspicious process activity
   journalctl -xe

1. Analyze Filesystem Changes:

• Look for unexpected directory renames
• Identify new bind mounts
• Check for modified sensitive files

1. Engage Incident Response:

• Preserve evidence
• Conduct full forensic analysis
• Determine scope of compromise
• Implement containment measures

References

Official Security Advisories:

• Linux Kernel Security Advisories: https://www.kernel.org/doc/html/latest/security/
• CVE-2025-68736 Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-68736
• NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2025-68736

Distribution-Specific Advisories:

• Red Hat Security Advisories: https://access.redhat.com/security/
• Ubuntu Security Notices: https://ubuntu.com/security/notices
• Debian Security Information: https://www.debian.org/security/
• SUSE Security Updates: https://www.suse.com/security/

Technical Documentation:

• Landlock Documentation: https://www.kernel.org/doc/html/latest/userspace-api/landlock.html
• Linux Kernel Mount Namespaces: https://man7.org/linux/man-pages/man7/mount_namespaces.7.html
• Audit Framework Documentation: https://access.redhat.com/documentation/en-us/redhatenterpriselinux/8/html/securityguide/auditing-the-system_security-guide

Related CVEs and Security Research:

• Landlock Security Module Overview
• Previous Landlock Vulnerabilities and Fixes
• Kernel Security Module Architecture

Document Version: 1.0
Last Updated: 2025
Classification: Security Advisory
Distribution: Internal Use / Authorized Recipients

For questions or additional information, contact your organization’s security team or system administration department.