A new vulnerability, tracked as CVE-2025-4598, has been discovered in systemd-coredump, the component responsible for collecting and processing core dumps on many modern Linux systems. This flaw allows an attacker to exploit a race condition by crashing a privileged SUID (Set-User-ID) process and quickly replacing it with a non-SUID binary—effectively stealing memory dumps (including secrets like /etc/shadow contents) from the original privileged process.

Read on to understand how this bug works, why it's dangerous, and see proof-of-concept details.

Why SUID Binaries Matter

SUID binaries (Set-User-ID) are programs given a special privilege: when run, they operate as the file’s owner (often root), even when started by an unprivileged user. This lets them access protected files and run powerful commands ordinary users cannot.

For example: /usr/bin/passwd (for changing your password) is SUID-root, so it can read and write directly to /etc/shadow (where hashed passwords live), even though ordinary users can’t.

Here’s where the problem arises

- When a SUID process crashes, systemd-coredump quickly takes a snapshot of its memory (the “core dump”) for debugging.
- This snapshot can reveal secrets stored in memory: passwords, tokens, and even copies of /etc/shadow.
- There’s a race window: If the SUID process is killed and the Linux kernel reuses its PID *before* systemd-coredump finishes its analysis, a fast attacker can start a new, normal (non-SUID) process using the same PID.
- Systemd-coredump may then operate on the new, unprivileged process, but using the data (core dump) from the privileged (SUID) process.

Result: the attacker can request and download the SUID process’s memory dump as an unprivileged user, with all its secrets.

Runs the SUID binary in a loop, forcing it to crash (e.g., using segmentation faults).

2. Quickly launches a dummy process after each crash, hoping it gets the same PID as the just-crashed SUID program (*"PID recycling"*).
3. If successful, the dumped memory for the SUID process becomes accessible to the attacker, as it's now tied to an unprivileged process's context.

Visual Attack Flow

Attacker triggers SUID binary crash 
         |
  Systemd gets notified, starts coredump process
         |
Linux kernel recycles PID quickly
         |
Attacker launches dummy binary with old PID
         |
Systemd-coredump processes dump as if it's for non-SUID binary
         |
Attacker reads SUID binary's secrets from core dump

Proof-of-Concept Exploit Snippet

*DISCLAIMER: This code is for educational use on test machines only! Never use on machines you don't own.*

Here’s a simplified example (exploit concept).

# suid-crash.sh
while true; do
    ./suid-victim &
    pid=$!
    sleep .01            # Fine-tune this timing for your system!
    kill -SEGV $pid       # Crash the SUID process
    # Try instantly to launch a dummy process with recycled PID
    ./non_suid_dummy &
done

A more targeted exploit may interact directly with systemd-coredump socket or files in /var/lib/systemd/coredump/.

Search for /etc/shadow entries inside the dump

strings /var/lib/systemd/coredump/core.suid-victim.* | grep root

The Vulnerable Code Patterns

The flaw lies in the window between SUID crash and coredump processing: systemd-coredump checks /proc/$PID/auxv (and similar paths) to learn about the process. If the PID is reused in that time, systemd-coredump gets the info from *the wrong process*.

This is called a race condition: the security of the system depends on the timing of two parallel events.

Real-World Risks

- Sensitive data leak: If an attacker wins the PID race even once, they can harvest information like root password hashes, SSH keys, or service tokens.

Fix & Mitigations

The systemd team is patching this by making systemd-coredump capture process state immediately, using file descriptors or pre-copying /proc data, instead of following PIDs that can be recycled.

Mitigations before an official patch

- Use core_pattern settings to limit core dumps or send them to a script that checks and restricts access.
- Restrict who can read files in /var/lib/systemd/coredump/.

References

- systemd GitHub Issue (Look for CVE-2025-4598 soon)
- Initial advisory (OSS-Security mailing list)
- Set-User-ID (SUID) explanation

Conclusion

CVE-2025-4598 shows why race conditions matter for security, especially with system privileged processes. If you maintain or use Linux servers—especially those exposing SUID binaries—update your systems once a patch is available, and consider restricting core dump access in the meantime.

Stay tuned for updates from your distribution’s security team.

Timeline

Published on: 05/30/2025 14:15:23 UTC
Last modified on: 06/05/2025 07:15:23 UTC