CVE-2022-20655 - ConfD CLI Command Injection Vulnerability Unveiled

Devices running ConfD—a widely used software for network configuration—were found vulnerable to a dangerous flaw (CVE-2022-20655) in how their CLI (Command Line Interface) processes certain inputs. This bug could let attackers, with local authenticated access, execute any command they want as the root user. Here, I’ll break down how this works, the risks, and provide a practical, easy-to-understand overview complete with real-world code snippets and reference links.

What Is ConfD?

First, for those not familiar: ConfD by Tail-f is a management solution used by many networking devices (routers, switches, etc.). It offers a powerful CLI and NETCONF/RESTCONF APIs for device management, and is often integrated into products by multiple vendors.

Location: Command Line Interface (CLI) argument parsing

- Who can exploit it? A local, authenticated user (like someone with shell or console access via SSH, serial, etc.)

What’s at risk? Arbitrary command execution as ConfD user (often root)

The vulnerability exists because ConfD’s CLI doesn’t properly sanitize arguments passed to certain internal processes. If an attacker can craft their input, they may insert extra shell commands, which the system then executes unintentionally.

Imagine you’re allowed to run a command like

show user-config username input_from_user

But, under the hood, the system runs this

/usr/confd/bin/show_user_config --username INPUT_FROM_USER

If the input isn’t sanitized, what if a clever attacker provides something like

alice; id; touch /tmp/hacked

That could result in

/usr/confd/bin/show_user_config --username alice; id; touch /tmp/hacked

Now, instead of just running the expected command, it also runs id (showing user info) and touch /tmp/hacked (creating a test file).

Exploit Example

Let’s walk through a very simplified proof of concept. Note: This is illustrative and generic, as actual details may vary per device integration.

`

device# show user-config username "bob; id > /tmp/confd_pwned"

`bash

/usr/confd/bin/show_user_config --username bob; id > /tmp/confd_pwned

Post-exploit:

The file /tmp/confd_pwned now holds the output of the id command, showing the attacker succeeded.

Let’s imagine what the code might look like inside ConfD

// Pseudocode for dangerous call
void show_user_config(char* username) {
    char command[256];
    snprintf(command, sizeof(command), "/usr/confd/bin/show_user_config --username %s", username);
    system(command); // <----- Vulnerable to injection!
}

The mistake: passing user input directly to the shell without sanitizing it.

If exploited, attackers can

- Read/download sensitive files

How to Protect Your Network

- Update: Check your vendor for patches addressing CVE-2022-20655. Cisco, for example, released advisories.
- Restrict CLI access: Only allow trusted users, and limit IP ranges and account privileges where possible.
- Monitor logs: Sudden use of system binaries or presence of unfamiliar files (like /tmp/confd_pwned) may indicate exploitation.

References

- NIST National Vulnerability Database: CVE-2022-20655
- Cisco Security Advisory for CVE-2022-20655
- Tail-f ConfD Official Product Page

Final Thoughts

Command injection vulnerabilities like CVE-2022-20655 are a sober reminder: even trusted, mature network software can have critical security lapses if user input isn’t strictly checked. If you manage systems running ConfD, patch quickly and check your user accounts. Always treat local device access with the same caution as remote exploits—especially when root is at stake.

Timeline

Published on: 11/15/2024 16:15:20 UTC