CVE-2023-29182 - Understanding the FortiOS Stack-Based Buffer Overflow Vulnerability

*Published: June 2024*

Summary

CVE-2023-29182 is a serious stack-based buffer overflow vulnerability (CWE-121) affecting several versions of Fortinet’s FortiOS, the operating system powering FortiGate firewalls. Discovered in early 2023 and patched in version 7..3, this flaw allows privileged users to execute arbitrary code on the device if they can bypass existing stack protections.

This post is a deep dive into CVE-2023-29182, its exploitation details, remediation, and how to safeguard your network. We use straightforward language and clear code examples to make it accessible, while providing direct links to advisories and further technical resources.

The Vulnerability at a Glance

Component: FortiOS – system CLI
Vulnerable Versions: FortiOS before 7..3
Attack Vector: Requires privileged CLI access
Attack Complexity: High (must bypass stack protections)

Official Advisory

- Fortinet PSIRT - CVE-2023-29182

How does the CVE-2023-29182 Bug Work?

This vulnerability is rooted in improper management of memory on the stack by the CLI command processor. When a user with sufficient privileges submits a carefully crafted command, the application copies more data onto the stack than it can safely hold—leading to a buffer overflow.

In most modern systems, stack protections like stack canaries or address randomization can mitigate such vulnerabilities. However, if an attacker can evade these protections (for instance, by leveraging another vulnerability), they can use CVE-2023-29182 to run their own code—potentially taking full control of the device.


### Code Snippet / Proof-of-Concept

Here’s a simplified C-like illustration of the vulnerable code pattern (not actual Fortinet source):

// Vulnerable function inside CLI handler

void handle_cli_input(char *input) {
    char buffer[200];
    // Unsafe: No bounds checking, possible overflow if input > 200 bytes
    strcpy(buffer, input);
    process_command(buffer);
}

An attacker could exploit this by submitting a command longer than 200 bytes. For example, in a CLI interface:

# input command with a long payload of 300 'A's
> myvulncmd AAAAAAAAA... (repeat 'A' 300 times)

The result? Stack memory is overwritten—possibly including the function return address. If the attacker can place a payload that hijacks execution, they can run arbitrary code on the firewall.

Required Conditions

- Attacker must have administrator-level CLI access (local or remote via SSH/Console).
- Existing stack protections (like stack canaries, ASLR) must be defeated. On some older hardware or misconfigured FortiOS systems, these defenses might be weak or not applied.
- "Privilege escalation" from another bug could boost a lower-privileged user to sufficient footing to attempt exploitation.

Stack Overflow: Carefully crafted input overwrites control data on the stack.

4. Execute Payload: The overwritten return pointer (or function pointer) redirects execution to malicious code the attacker placed on the stack or elsewhere in memory.

NOTE: No public Metasploit module or weaponized exploit has been released for CVE-2023-29182 as of June 2024, reflecting its complexity and the need to bypass strong OS protections.

Real-World Mitigation

Fortinet fixed this flaw in FortiOS 7..3 and later.

If you haven’t upgraded, do it ASAP.

Vendor Patch:
- Download latest FortiOS

Upgrade: Move to FortiOS 7..3 or later.

- Restrict Admin Access: Limit CLI/admin access to trusted IPs.

Monitor Logs: Watch for unusual or oversize commands in logs.

- Enable Strong Stack Protections: If possible, validate OS/compiler mitigation settings.

Further Resources

- NVD Entry - CVE-2023-29182
- Fortinet Security Advisory Archive
- MITRE CWE-121 - Stack-based Buffer Overflow
- What Is Stack Overflow? (OWASP)

Final Thoughts

CVE-2023-29182 is a great example of how classic programming bugs—like improper use of strcpy on the stack—can persist for years, but only become exploitable with the right conditions. In the hands of an attacker who already has privileged access, even a single overlooked buffer check can spell disaster.

Stay safe:
Patch early, restrict admin access, and keep an eye on security news for all devices on your perimeter!


*This write-up is exclusive content, using plain explanations and practical tips. Share with colleagues to help keep your infrastructure secure!*

Timeline

Published on: 08/17/2023 10:15:00 UTC
Last modified on: 08/23/2023 15:36:00 UTC