CVE-2024-24195 - Critical Misaligned Address Vulnerability in robdns (Commit d76d2e6) Explored
A newly disclosed vulnerability, CVE-2024-24195, was found in the open-source DNS software robdns, specifically in commit d76d2e6. The issue lies in a misaligned address found in the source file /src/zonefile-insertion.c. In this article, we’ll break down what this means, why it matters, and how it can be exploited, all in simple terms. We'll also show you some code snippets and give pointers to original sources.
What is robdns?
robdns is a lightweight and high-performance DNS server, popular for its simple design and use in research or minimal production environments. It's written in C, which means it's fast, but also potentially vulnerable to memory management issues.
Where’s the Vulnerability?
The problem was found in a specific commit, d76d2e6, and reported as CVE-2024-24195. The issue is a misaligned address when handling zonefile data, specifically in zonefile-insertion.c. In C, memory alignment is crucial: reading or writing to misaligned addresses can cause crashes or even let attackers run code they shouldn’t.
How Does the Vulnerability Work?
When code accesses memory, it expects that data is aligned in a certain way. If it isn't (for example, a 32-bit value isn’t on a 4-byte boundary), you can get undefined behavior, which is a gold mine for hackers.
The vulnerable code looks roughly like this
// zonefile-insertion.c: simplified illustration
uint16_t *type = (uint16_t *)(p + 2); // p might not be 2-byte aligned!
If p + 2 isn’t properly aligned, dereferencing it as a uint16_t * can crash the process or, in the right/wrong circumstances, lead to remote code execution.
Real Exploit Example
To exploit this, an attacker could craft a DNS zonefile with carefully structured data to trigger the bug during parsing. Here’s how a minimal exploit might look:
# Sample exploit: prepare a misaligned zonefile
with open("exploit.zone", "wb") as f:
f.write(b"\x00" * 3) # 3 bytes to make misalignment
f.write(b"\x01\x02") # fake record that gets misaligned
Load this zonefile in robdns (affected commit), and you may see a segmentation fault, demonstrating the bug.
Impact
- Denial of Service (DoS): The most straightforward impact is that robdns can be crashed remotely simply by feeding it a crafted zonefile.
- Potential for RCE: In some cases, attackers might be able to exploit the misaligned access to run arbitrary code (although reproducing this is system- and architecture-dependent).
Fix and Mitigation
The simplest fix is to avoid directly casting pointers to aligned types. Use memcpy or similar safe methods:
// Safe pattern
uint16_t type;
memcpy(&type, p + 2, sizeof(type));
Always ensure that your pointers are correctly aligned before dereferencing them as a particular type.
Official commit reference:
CVE entry:
Intro to alignment bugs:
Stack Overflow: What does “128-bit aligned” mean?
Conclusion
CVE-2024-24195 serves as a reminder that even modern, small C projects like robdns can harbor serious vulnerabilities from low-level issues like misaligned memory. If you use robdns, update to a patched version or audit your usage of zonefiles. Memory safety matters—one misaligned pointer can bring your server down or worse.
Have more questions or want to share experiences? Drop your thoughts below or follow the latest updates from robdns on GitHub.
Timeline
Published on: 06/06/2024 22:15:10 UTC
Last modified on: 10/29/2024 18:24:07 UTC