Entries Tagged "zero-day"

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Claude Mythos Has Found 271 Zero-Days in Firefox

That’s a lot. No, it’s an extraordinary number:

Since February, the Firefox team has been working around the clock using frontier AI models to find and fix latent security vulnerabilities in the browser. We wrote previously about our collaboration with Anthropic to scan Firefox with Opus 4.6, which led to fixes for 22 security-sensitive bugs in Firefox 148.

As part of our continued collaboration with Anthropic, we had the opportunity to apply an early version of Claude Mythos Preview to Firefox. This week’s release of Firefox 150 includes fixes for 271 vulnerabilities identified during this initial evaluation.

As these capabilities reach the hands of more defenders, many other teams are now experiencing the same vertigo we did when the findings first came into focus. For a hardened target, just one such bug would have been red-alert in 2025, and so many at once makes you stop to wonder whether it’s even possible to keep up.

Our experience is a hopeful one for teams who shake off the vertigo and get to work. You may need to reprioritize everything else to bring relentless and single-minded focus to the task, but there is light at the end of the tunnel. We are extremely proud of how our team rose to meet this challenge, and others will too. Our work isn’t finished, but we’ve turned the corner and can glimpse a future much better than just keeping up. Defenders finally have a chance to win, decisively.

They’re right. Assuming the defenders can patch, and push those patches out to users quickly, this technology favors the defenders.

News article.

Posted on April 29, 2026 at 6:12 AM • View Comments

AI Found Twelve New Vulnerabilities in OpenSSL

The title of the post is”What AI Security Research Looks Like When It Works,” and I agree:

In the latest OpenSSL security release> on January 27, 2026, twelve new zero-day vulnerabilities (meaning unknown to the maintainers at time of disclosure) were announced. Our AI system is responsible for the original discovery of all twelve, each found and responsibly disclosed to the OpenSSL team during the fall and winter of 2025. Of those, 10 were assigned CVE-2025 identifiers and 2 received CVE-2026 identifiers. Adding the 10 to the three we already found in the Fall 2025 release, AISLE is credited for surfacing 13 of 14 OpenSSL CVEs assigned in 2025, and 15 total across both releases. This is a historically unusual concentration for any single research team, let alone an AI-driven one.

These weren’t trivial findings either. They included CVE-2025-15467, a stack buffer overflow in CMS message parsing that’s potentially remotely exploitable without valid key material, and exploits for which have been quickly developed online. OpenSSL rated it HIGH severity; NIST‘s CVSS v3 score is 9.8 out of 10 (CRITICAL, an extremely rare severity rating for such projects). Three of the bugs had been present since 1998-2000, for over a quarter century having been missed by intense machine and human effort alike. One predated OpenSSL itself, inherited from Eric Young’s original SSLeay implementation in the 1990s. All of this in a codebase that has been fuzzed for millions of CPU-hours and audited extensively for over two decades by teams including Google’s.

In five of the twelve cases, our AI system directly proposed the patches that were accepted into the official release.

AI vulnerability finding is changing cybersecurity, faster than expected. This capability will be used by both offense and defense.

More.

Posted on February 18, 2026 at 7:03 AM • View Comments

LLMs are Getting a Lot Better and Faster at Finding and Exploiting Zero-Days

This is amazing:

Opus 4.6 is notably better at finding high-severity vulnerabilities than previous models and a sign of how quickly things are moving. Security teams have been automating vulnerability discovery for years, investing heavily in fuzzing infrastructure and custom harnesses to find bugs at scale. But what stood out in early testing is how quickly Opus 4.6 found vulnerabilities out of the box without task-specific tooling, custom scaffolding, or specialized prompting. Even more interesting is how it found them. Fuzzers work by throwing massive amounts of random inputs at code to see what breaks. Opus 4.6 reads and reasons about code the way a human researcher would­—looking at past fixes to find similar bugs that weren’t addressed, spotting patterns that tend to cause problems, or understanding a piece of logic well enough to know exactly what input would break it. When we pointed Opus 4.6 at some of the most well-tested codebases (projects that have had fuzzers running against them for years, accumulating millions of hours of CPU time), Opus 4.6 found high-severity vulnerabilities, some that had gone undetected for decades.

The details of how Claude Opus 4.6 found these zero-days is the interesting part—read the whole blog post.

News article.

Posted on February 9, 2026 at 7:04 AM • View Comments

Zero-Day Exploit in WinRAR File

A zero-day vulnerability in WinRAR is being exploited by at least two Russian criminal groups:

The vulnerability seemed to have super Windows powers. It abused alternate data streams, a Windows feature that allows different ways of representing the same file path. The exploit abused that feature to trigger a previously unknown path traversal flaw that caused WinRAR to plant malicious executables in attacker-chosen file paths %TEMP% and %LOCALAPPDATA%, which Windows normally makes off-limits because of their ability to execute code.

More details in the article.

Posted on August 19, 2025 at 7:07 AM • View Comments

Microsoft SharePoint Zero-Day

Chinese hackers are exploiting a high-severity vulnerability in Microsoft SharePoint to steal data worldwide:

The vulnerability, tracked as CVE-2025-53770, carries a severity rating of 9.8 out of a possible 10. It gives unauthenticated remote access to SharePoint Servers exposed to the Internet. Starting Friday, researchers began warning of active exploitation of the vulnerability, which affects SharePoint Servers that infrastructure customers run in-house. Microsoft’s cloud-hosted SharePoint Online and Microsoft 365 are not affected.

Here’s Microsoft on patching instructions. Patching isn’t enough, as attackers have used the vulnerability to steal authentication credentials. It’s an absolute mess. CISA has more information. Also these four links. Two Slashdot threads.

This is an unfolding security mess, and quite the hacking coup.

Posted on July 28, 2025 at 7:09 AM • View Comments

Most of 2023’s Top Exploited Vulnerabilities Were Zero-Days

Zero-day vulnerabilities are more commonly used, according to the Five Eyes:

Key Findings

In 2023, malicious cyber actors exploited more zero-day vulnerabilities to compromise enterprise networks compared to 2022, allowing them to conduct cyber operations against higher-priority targets. In 2023, the majority of the most frequently exploited vulnerabilities were initially exploited as a zero-day, which is an increase from 2022, when less than half of the top exploited vulnerabilities were exploited as a zero-day.

Malicious cyber actors continue to have the most success exploiting vulnerabilities within two years after public disclosure of the vulnerability. The utility of these vulnerabilities declines over time as more systems are patched or replaced. Malicious cyber actors find less utility from zero-day exploits when international cybersecurity efforts reduce the lifespan of zero-day vulnerabilities.

Posted on November 18, 2024 at 10:49 AM • View Comments

AIs Discovering Vulnerabilities

I’ve been writing about the possibility of AIs automatically discovering code vulnerabilities since at least 2018. This is an ongoing area of research: AIs doing source code scanning, AIs finding zero-days in the wild, and everything in between. The AIs aren’t very good at it yet, but they’re getting better.

Here’s some anecdotal data from this summer:

Since July 2024, ZeroPath is taking a novel approach combining deep program analysis with adversarial AI agents for validation. Our methodology has uncovered numerous critical vulnerabilities in production systems, including several that traditional Static Application Security Testing (SAST) tools were ill-equipped to find. This post provides a technical deep-dive into our research methodology and a living summary of the bugs found in popular open-source tools.

Expect lots of developments in this area over the next few years.

This is what I said in a recent interview:

Let’s stick with software. Imagine that we have an AI that finds software vulnerabilities. Yes, the attackers can use those AIs to break into systems. But the defenders can use the same AIs to find software vulnerabilities and then patch them. This capability, once it exists, will probably be built into the standard suite of software development tools. We can imagine a future where all the easily findable vulnerabilities (not all the vulnerabilities; there are lots of theoretical results about that) are removed in software before shipping.

When that day comes, all legacy code would be vulnerable. But all new code would be secure. And, eventually, those software vulnerabilities will be a thing of the past. In my head, some future programmer shakes their head and says, “Remember the early decades of this century when software was full of vulnerabilities? That’s before the AIs found them all. Wow, that was a crazy time.” We’re not there yet. We’re not even remotely there yet. But it’s a reasonable extrapolation.

EDITED TO ADD: And Google’s LLM just discovered an exploitable zero-day.

Posted on November 5, 2024 at 7:08 AM • View Comments

Using LLMs to Exploit Vulnerabilities

Interesting research: “Teams of LLM Agents can Exploit Zero-Day Vulnerabilities.”

Abstract: LLM agents have become increasingly sophisticated, especially in the realm of cybersecurity. Researchers have shown that LLM agents can exploit real-world vulnerabilities when given a description of the vulnerability and toy capture-the-flag problems. However, these agents still perform poorly on real-world vulnerabilities that are unknown to the agent ahead of time (zero-day vulnerabilities).

In this work, we show that teams of LLM agents can exploit real-world, zero-day vulnerabilities. Prior agents struggle with exploring many different vulnerabilities and long-range planning when used alone. To resolve this, we introduce HPTSA, a system of agents with a planning agent that can launch subagents. The planning agent explores the system and determines which subagents to call, resolving long-term planning issues when trying different vulnerabilities. We construct a benchmark of 15 real-world vulnerabilities and show that our team of agents improve over prior work by up to 4.5×.

The LLMs aren’t finding new vulnerabilities. They’re exploiting zero-days—which means they are not trained on them—in new ways. So think about this sort of thing combined with another AI that finds new vulnerabilities in code.

These kinds of developments are important to follow, as they are part of the puzzle of a fully autonomous AI cyberattack agent. I talk about this sort of thing more here.

Posted on June 17, 2024 at 7:08 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.