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If you’ve ever stared into the abyss of a legacy C codebase and thought, “Well, that’s a buffer overflow just waiting to happen,” congratulations—you’ve met wirespy. And if you’ve ever wished for an AI sidekick that could actually understand the nuances of security flaws without nagging you about semicolons, let me introduce you to Claude Code.

I recently ran this agentic command-line wonder from Anthropic through the wringer by pointing it at my own code (wirespy), a network sniffer I wrote that operates as a daemon, captures live traffic, and occasionally flirts with danger by running as root.

What Is wirespy?

In short: It’s a C-based network packet analysis tool built for extracting juicy metadata and generating firewall and NetFlow logs. Think tcpdump meets “I want to break things responsibly.”

But here’s the kicker: it processes raw, untrusted packets while running with elevated privileges. It’s like giving your teenager the keys to a Ferrari and telling them not to speed. You know what’s going to happen.

From the README.md, I even admit:

“Assume that there are errors in the wsd source that would allow a specially crafted packet to allow an attacker to exploit wsd to gain access to the computer that wsd is running on!!!”

Yes, triple exclamation marks. This is C, after all. Every exclamation is earned.

Why wirespy Is a Perfect Target for Claude

If you’re looking for a testbed full of real-world security sins—unchecked memory, file I/O, raw socket access, and enough pointer arithmetic to summon undefined behavior from the void, wirespy delivers.

• Runs as root? Yep.
• Parses raw packets? Of course.
• Manually allocates memory like it’s 1995? You bet.
• Has edge-case bugs waiting to become CVEs? We’re practically handing them out like candy.

Setting Up Claude Code for the Hunt

Deploying Claude Code is refreshingly simple:

git clone https://github.com/rondilley/wirespy.git
cd wirespy
claude-code "Analyze this C codebase for security vulnerabilities, focusing on buffer overflows, input validation, and memory safety issues"

That prompt alone had Claude sweating through its synthetic shirt. But to its credit, it didn’t flinch.

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Top Bugs Found (and Squashed) with Claude Code

1. Buffer Overflow in Packet Parsing

Vulnerable Code:

char packet_buffer[1024];
memcpy(packet_buffer, packet_data, packet_length); // Who needs bounds checking, right?

Claude’s Fix:

size_t copy_length = (packet_length > sizeof(packet_buffer) - 1) ? sizeof(packet_buffer) - 1 : packet_length;
memcpy(packet_buffer, packet_data, copy_length);
packet_buffer[copy_length] = '\0';

Apparently, “crashing gracefully” isn’t a viable security model anymore. Who knew?

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2. Format String Vulnerability

Bad Code:

syslog(LOG_INFO, packet_content); // Great way to let attackers log whatever they want. %-sabotage, anyone?

Fix:

syslog(LOG_INFO, "Packet content: %s", packet_content);

Stop letting user input write your logs—or your obituary.

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3. Integer Overflow in Allocation

Classic Fail:

size_t total_size = num_packets * max_packet_size;
buffer = malloc(total_size);

Fixed Like a Pro:

if (num_packets > SIZE_MAX / max_packet_size) return -1;
buffer = malloc(num_packets * max_packet_size);

Overflow bugs: the silent killers of C.

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4. Race Condition in Signal Handling

Bug:
Signal handlers modifying shared state without synchronization. Somewhere, a use-after-free is laughing.

Resolution:

volatile sig_atomic_t shutdown_requested = 0;
void signal_handler(int sig) { shutdown_requested = 1; }

C may not give you mutexes for signals, but it does give you enough rope to hang your daemon.

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Claude Code’s Secret Sauce

What makes Claude Code different from traditional static analyzers? Here’s what stood out:

• Understands Context: It doesn’t just say “you have a bug”, it knows the security impact of that bug in a privileged daemon parsing external input.
• Suggests Real Fixes: Not just “hey, that’s dangerous,” but actual mitigations that maintain function.
• Finds the Subtle Stuff: Integer overflows and race conditions aren’t flashy, but they’ll ruin your weekend.
• Helps Build Test Suites: I had it generate fuzzing cases post-fix. The AI practically started doing threat modeling while I sipped coffee.

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Post-Fix Testing with Claude

Prompt:

claude-code "Generate fuzzing test cases for the packet parsing functions we just secured..."

Output:

• Packets with malformed headers
• Strings loaded with rogue %n format specifiers
• Edge-case packet sizes designed to trigger overflow
• Simulated signals during processing

In other words: everything your average bored adversary might throw at it. And probably your intern too.

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Hardened wirespy: v0.8 Security Upgrades

• Privilege Dropping: Starts as root, but then drops like a bad habit.
• Chroot Support: Because isolation is a virtue.
• Input Validation: Every byte checked like it’s showing up at TSA.
• Safe String Ops: No more strcpy roulette.

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Best Practices for Using Claude Code in Security Audits

1. Define Your Scope: Be specific—buffer overflows? Race conditions? Memory safety?
2. Provide Context: Tell it how the software runs so it can prioritize.
3. Iterate Fixes: Have Claude review your fix before you commit your next oopsie.
4. Auto-generate Tests: If you’re not testing edge cases, you’re not testing.
5. Document Everything: Claude will happily help you explain what the fix does and why it matters.

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Final Thoughts

Claude Code isn’t magic. It’s not a replacement for human expertise (but it’s a damn good augmentation layer). Especially for C codebases like wirespy that are equal parts useful and terrifying.

Using Claude on this project reminded me that good security tooling should feel like a partner, not a nag. It caught subtle bugs, recommended clear fixes, and even wrote test cases without me having to bribe it with coffee.

So if you’re writing C code that sniffs packets, handles input, or gasp runs as root—consider Claude Code your new best frenemy.

You can grab wirespy on GitHub, and Claude Code is available in research preview from Anthropic.

Go break your own code before someone else does it for you.

—Ron Dilley
Cybersecurity Curmudgeon (In Training), Adversary Agitator, C Code Evangelist