Anthropic: Latest Claude model finds more than 500 vulnerabilities

Anthropic claims its latest Claude large language model (LLM), Claude Opus 4.6, discovered more than 500 validated high-severity vulnerabilities, according to a report published Thursday.

Claude Opus 4.6, which was released to the public Feb. 5, 2026, reportedly discovered hundreds of vulnerabilities in open-source software while working in a virtual machine with access to utilities and tools, such as coreutils and fuzzers.

Anthropic said Claude worked “out-of-the-box” without custom harnesses to search for memory corruption vulnerabilities in the latest versions of several open-source projects. The bugs discovered by Claude were then reviewed and validated by human researchers to weed out hallucinations and false positives, the company said.

Vulnerabilities reported and resolved by project maintainers include a stack buffer underflow vulnerability in GhostScript, and buffer overflow vulnerabilities in OpenSC and CGIF.  

For the vulnerability in GhostScript, which is a utility for processing PostScript and PDF files, Claude first attempted fuzzing and manual analysis, which yielded no results. However, it ultimately identified the vulnerability by examining previous security-related commits and searching for flaws that were similar to one that was already fixed.

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Claude also identified the flaw in OpenSC, a command line utility used for processing smart card data, not through fuzzing or manual analysis, but by searching for frequently vulnerable function calls and identifying an area of code with multiple successive srtcat operations.

In CGIF, a library for processing GIF images, Claude discovered an edge case involving LZW compression where a compressed image could be larger than its corresponding uncompressed image. Anthropic noted that validating this flaw required an understanding of LZW compression and a specific sequence of steps that would not be possible to achieve through traditional fuzzing.

Anthropic said it is continuing to validate, report and develop patches for Claude-discovered bugs, noting, “Many of these projects are maintained by small teams or volunteers who don’t have dedicated security resources, so finding human-validated bugs and contributing human-reviewed patches goes a long way.”

The company said it is also introducing additional safeguards to prevent the misuse of Claude by cyber threat actors, including cyber-specific “probes” that monitor model activations during response generation to detect potentially harmful responses.

Anthropic said it may also expand the actions it takes in response to misuse, including by implementing real-time intervention to block potentially malicious traffic.

“This will create friction for legitimate research and some defensive work, and we want to work with the security research community to find ways to address it as it arises,” Anthropic said.

The company reported last year that its Claude Code tool was used in a sophisticated cyberattack campaign by suspected China-sponsored threat actors, targeting about 30 organizations worldwide.

Anthropic joins several companies that have touted the ability of LLMs to speed vulnerability research, with Google debuting its “Big Sleep” agent in 2024 and Microsoft announcing in April 2025 that its Security Copilot aided in the discovering of 20 open-source bootloader flaws.