Scan Your Codebase for Mythos-Class Vulnerabilities in 5 Minutes

#security #ai #tutorial

By Jeremie Strand, co-founder at SkillSafe.AI

The threat is real and already priced

This week, Anthropic published results from Mythos, their frontier AI model with full offensive security capabilities. The findings are worth sitting with: a 27-year-old signed integer overflow in OpenBSD's TCP SACK implementation, discovered for under $50. A 16-year-old out-of-bounds heap write in FFmpeg's H.264 decoder -- slice counter collision, roughly $10k across runs. A 17-year-old FreeBSD NFS RCE, CVE-2026-4747 -- stack buffer overflow in RPCSEC_GSS, unauthenticated root access. These aren't theoretical. They're sitting in production systems right now.

Over 99% of what Mythos discovered remains unpatched. The model found 595 tier-1 and tier-2 crashes and 10 tier-5 full control-flow hijacks -- compared to 150-175 for prior models. It produced 181 working Firefox exploits versus 2 for Opus 4.6. Browser sandbox escapes via 4-vulnerability chains. Linux privilege escalation chains under $2,000 each. Human experts require weeks for equivalent analysis; Mythos does it in hours at a fraction of the cost. Full writeup: https://red.anthropic.com/2026/mythos-preview/

The asymmetry is the problem. Attackers need one flaw. You need to have covered everything. A $50 bug in a 27-year-old code path is just as exploitable as a freshly disclosed CVE. And the economics are only going to get more lopsided.

The defender's response

There's a structured way to think about this. The SkillSafe playbook (https://skillsafe.ai/blog/claude-mythos-zero-days-defender-playbook/) lays out a four-part framework: scan code like attackers would, patch aggressively, audit dependencies beyond just your own code, and assume internet-facing services will be probed. This tutorial covers step one -- getting a real scanner running against your codebase in the next five minutes.

Install

Send these to your AI agent

Create the skillsafe skill from https://skillsafe.ai/skill.md

and then

install @jeremie-strand/security-scanner from skillsafe.ai

Works with any AI agent that supports skills -- Claude Code, Cursor, Windsurf, Cline, and others. The skill is cryptographically verified on install and security-scanned before publication in the SkillSafe registry.

Run it

/security-scanner

The scanner runs CWE-mapped pattern detection across your source code, checks your dependency tree against known CVE databases, and scans container configurations for known vulnerable base images and misconfigurations.

Sample output:

[security-scanner] Scanning /src...

FINDING: CWE-79 (XSS) -- src/api/render.js:142
  Unescaped user input passed to innerHTML
  Severity: HIGH

FINDING: Outdated dependency -- package.json
  lodash@4.17.15 -- CVE-2021-23337 (prototype pollution, CVSS 7.2)
  Fix: upgrade to 4.17.21+

FINDING: Container base image
  node:16-alpine -- EOL, last patched 2024-04-30
  Known CVEs: 4 (1 critical)

Summary: 3 findings (1 high, 1 medium, 1 informational)
Scan completed in 14s

The CWE mapping is what separates this from grepping for "eval(". Each finding is categorized against the Common Weakness Enumeration taxonomy -- the same framework security researchers and CVE databases use -- so you can triage by type, not just severity score.

What it checks

CWE-mapped code patterns -- injection, XSS, path traversal, insecure deserialization, and others from the CWE Top 25
Dependency age and known CVEs -- across npm, pip, cargo, go.sum, and other lockfile formats
Container vulnerabilities -- base image CVEs, exposed ports, privilege escalation paths
Known backdoor patterns from Mythos-class disclosures -- integer overflow patterns, RPCSEC_GSS-style stack buffer handling, heap write patterns from H.264-type parsers

The cost math

Mythos found a 27-year-old zero-day for $50. Running this scanner costs less. The same economic shift that makes AI-powered offense cheap also makes AI-powered defense cheap -- you get the same leverage. The difference is that attackers need to do this once to get in; you need to do it continuously to stay ahead. A scanner you run today catches the dependency that was fine last week and has a published CVE this morning. That's the job.