curl says Anthropic’s Mythos found one real flaw

curl maintainer Daniel Stenberg said Anthropic’s Mythos model found one confirmed vulnerability and about 20 bugs in curl after the project reviewed an AI-generated security report.

In a blog post, Stenberg described the finding as part of an ongoing series of AI-assisted scans of the curl codebase. He said curl had already been reviewed by other AI tools, including AISLE, Zeropath and OpenAI’s Codex Security, and that those earlier reviews had led to roughly 200 to 300 merged bug fixes over the past eight to 10 months.

The Mythos scan was arranged through Anthropic’s project Glasswing and the Linux Foundation’s Alpha Omega project, which helped connect open source projects with access to the model. Stenberg said he initially signed a contract for direct access, but that did not happen on schedule, so someone else with access ran the analysis and sent the report instead. He said that was good enough for curl’s purposes.

According to Stenberg, the report reviewed curl’s Git repository at a recent commit and analyzed about 178,000 lines of code in the src/ and lib/ directories. The report itself said curl is “one of the most fuzzed and audited C codebases in existence,” and noted that it did not find problems in the project’s hot paths, including HTTP/1, TLS and URL parsing.

curl’s security team did not accept the Mythos report at face value. Stenberg said the report listed five “confirmed security vulnerabilities,” but after several hours of review the team reduced that to one confirmed issue. He said three of the other findings were false positives tied to documented API behavior, and the fourth was treated as a bug rather than a vulnerability.

The one confirmed vulnerability is scheduled to become a low-severity CVE in curl 8.21.0, which Stenberg said is planned for late June. He did not publish the technical details yet, saying they will be disclosed when the release ships.

The report also identified about 20 additional bugs that were not classified as vulnerabilities. Stenberg said the curl team is investigating them one by one and fixing the ones it agrees with. He said the report contained very few false positives, which suggests the model had a high threshold for certainty.

Stenberg used the post to push back on the idea that Mythos is unusually dangerous or uniquely powerful. He said the result looked more like strong marketing than a major step change in code analysis, at least on curl. Even so, he said the report was useful and that AI code analyzers in general are now materially better than traditional tools at finding bugs and security flaws in source code.

He pointed to a few areas where AI tools help: they can catch mismatches between comments and code, reason about platforms or configurations that are hard to test directly, understand library and protocol behavior, explain findings clearly, and sometimes propose patches. He also said these tools keep finding the established classes of bugs rather than inventing entirely new ones.

Stenberg closed by saying the work is not finished. More security reports have already arrived while he was drafting the post, and he expects further AI scans to keep uncovering issues in curl and other projects.