If you’ve managed dial-up connections or even just played with old-school network tools, you might have come across ppp (Point-to-Point Protocol). It’s one of those ancient but surprisingly persistent tools used for network connections — especially on Unix and Linux systems.

Recently, a big problem surfaced: CVE-2024-58250. This long, clunky number stands for a real vulnerability in the *passprompt plugin* for pppd (the Point-to-Point Protocol Daemon), specifically in versions before 2.5.2. If you’re running a Linux or Unix-like server or workstation with PPP support enabled, read on — you may be exposed without realizing it.

Let’s break down what happened, why it matters, and how attackers could exploit it. We’ll also look at the code, and provide extra resources if you need to read further.

In plain English

> The passprompt plugin in pppd (that’s the daemon part of PPP) didn’t handle system privileges correctly in certain situations. That means when asking for a password in interactive authentication, it ran code with more privileges than it needed. That’s a violation of least privilege — the core security principle that says, “Only give code exactly as much power as it absolutely requires.”

A local attacker — someone with a regular user account — could exploit this mismanagement to potentially escalate their privileges or otherwise mess with your machine.

Technical Details

The passprompt plugin lets you interactively supply a password for PPP-based connections. To do this, it may *temporarily* invoke functions as the root user (uid=), but it doesn’t always drop those elevated rights before performing certain operations.

If any malicious code, plugin, or input gets handled during this timeframe, the code runs with full root privileges — a classic recipe for local privilege escalation.

Here’s a conceptual code snippet (not actual plugin code, but illustrative)

void prompt_for_pass() {
    seteuid(); // Switch to root privileges

    /* ...prompt the user for input... */
    printf("Enter PPP password: ");
    gets(user_input);        // Uh-oh: unsafe function
    // Do something with user_input

    seteuid(real_uid);       // Drop privileges - sometimes forgotten
}

Now, imagine if there’s any unsafe input or if seteuid(real_uid); isn’t always called, or called too late. For example, plugins might be loaded, logs might be written, or helper programs might get executed — all while still running as root!

Attackers would love this: once your code is running as root, it can do anything.

3. How Would an Attacker Exploit CVE-2024-58250?

- Local exploitation: An attacker with a normal user shell could trigger pppd using the passprompt plugin, possibly feeding malicious input.
- If code like system() or even just file writes happen _before_ dropping privileges, it could overwrite system files, create new SUID binaries, or spawn a privileged shell.

On multi-user systems, this could mean a quick and silent privilege escalation.

No public exploit code is available yet (as of this writing), but the bug is straightforward enough that writing a proof-of-concept would be easy for a capable attacker.

4. Who’s Affected?

- Anyone running ppp < 2.5.2 with the passprompt plugin enabled (often found on older servers, some embedded Linux boxes, routers, or legacy remote access setups).

Check your version

pppd --version

## 5. How To Fix / Protect Yourself

- Upgrade immediately. Version 2.5.2 fixes the problem. Download the latest release here.
- Disable the passprompt plugin if you don’t need interactive password authentication for PPP connections.

Official References

- Debian Security Advisory DSA-XXXXX
- Red Hat CVE Page for CVE-2024-58250 (Replace with official URL when available)
- PPPD Project on Salsa (Upstream Source)

6. TL;DR

- CVE-2024-58250: passprompt plugin in pppd (< 2.5.2) mishandles privileges; attackers can potentially root your system via local shell access.

Upgrade to 2.5.2 ASAP, and disable interactive password plugins if possible.

- More info: NVD CVE entry

Stay secure! Old code, old problems – don’t let legacy PPP bite you in 2024.

*This deep dive was written for security admins and Linux tinkerers. Share and spread awareness — vulnerabilities like this love to hide in little-used corners of your servers!*


For further discussion, see the upstream commit fixing the issue (URL may update as patch lands). If you have legacy PPP dial-up, it's time for a checkup!

Timeline

Published on: 04/22/2025 01:15:17 UTC
Last modified on: 04/23/2025 14:08:13 UTC