Mozilla has fixed 271 security vulnerabilities in Firefox after Anthropic’s Claude Mythos AI identified them during early testing.
Quick Summary – TLDR:
- Claude Mythos AI discovered 271 vulnerabilities in Firefox’s latest version.
- Firefox 150 includes fixes for these issues, with over 40 tracked as CVEs.
- AI matches elite human researchers but works much faster and at scale.
- Restricted access raises concerns about misuse in cyberattacks.
What Happened?
Mozilla revealed that an early version of Claude Mythos Preview helped uncover hundreds of hidden vulnerabilities in Firefox. These findings were addressed in the newly released Firefox 150, marking one of the largest AI-assisted security sweeps in a mainstream browser.
The discovery highlights how advanced AI models are rapidly transforming vulnerability detection, allowing teams to uncover issues that would otherwise take months of manual effort.
Anthropic’s recent announcement about using AI to enhance cybersecurity faced skepticism. However, Mozilla provided details supporting the use of its Claude Mythos Preview model to safeguard critical services.
— Nova Pov (@NovaPovNP) April 22, 2026
Mythos enabled Mozilla’s team to identify and fix 271… pic.twitter.com/vvIi4dwciT
AI Finds Hundreds of Hidden Bugs
The collaboration between Mozilla and Anthropic led to the identification of 271 vulnerabilities in Firefox’s codebase. While only a small portion of these were classified as high severity and assigned CVE identifiers, the majority still contributed to improving the browser’s overall security posture.
Many of the detected issues fall into categories such as:
- Low severity bugs and hardening gaps.
- Defense in depth improvements.
- Non exploitable code path flaws.
Despite their lower severity, these fixes strengthen Firefox against complex, multi-step attacks that rely on chaining smaller weaknesses together.
From 22 Bugs to 271: A Massive Leap
This is not Mozilla’s first experiment with AI-driven security. Earlier tests using Claude Opus 4.6 uncovered just 22 security sensitive bugs in Firefox 148.
The jump to 271 vulnerabilities with Mythos shows how quickly AI capabilities are evolving. According to Mozilla, the new model can reason through code in ways that were not possible just months ago.
As Firefox CTO Bobby Holley explained, computers were previously unable to match human level reasoning in vulnerability discovery, but that gap is now closing fast.
AI Matches Human Experts, But Faster
Mozilla emphasized that Mythos did not uncover any entirely new category of vulnerabilities. Every issue it found could have been identified by an elite human researcher.
However, the key advantage is speed and scale.
Instead of relying on limited human expertise, AI can:
- Analyze vast codebases quickly.
- Identify logic based vulnerabilities that traditional tools miss.
- Reduce months of work into days or weeks.
Cybersecurity firm Palo Alto Networks reported that Mythos achieved the equivalent of a year of penetration testing in under three weeks, highlighting its efficiency.
A Turning Point for Cyber Defense
Mozilla described this moment as a shift in the long standing balance between attackers and defenders. Traditionally, attackers had the advantage because they only needed to find one exploitable flaw.
With AI like Mythos, defenders may finally gain ground.
The company believes that making vulnerability discovery cheaper and faster could reduce the effectiveness of costly zero-day exploits, which have historically been reserved for well funded threat actors.
Concerns Around Misuse and Access
Despite its promise, Mythos raises serious concerns. Tools capable of identifying vulnerabilities at scale could also be used by malicious actors to automate cyberattacks.
To reduce this risk, Anthropic has limited access to the model through its Project Glasswing program. Participating organizations include major tech players such as:
- Amazon
- Apple
- Microsoft
Even with these restrictions, there are early reports suggesting unauthorized access may already be happening, adding urgency to the debate around AI safety.
SQ Magazine’s Takeaway
I see this as a real turning point in cybersecurity. For years, defenders have been stuck reacting to threats, always one step behind attackers. Now, tools like Mythos are changing that equation.
What stands out to me is not just the number of bugs found, but the speed. If AI can compress months of security work into weeks, companies that ignore this shift will fall behind quickly. At the same time, the risk is very real. The same power that helps defenders can easily be turned against them.
This is where things get interesting. Cybersecurity is no longer just about tools, it is about who gets access to the most powerful AI first.
