Anthropic's red team has Claude shrink attack surface instead of hunting individual bugs, and reports 493 issues across 25 projects

Anthropic ran Claude over 25 open-source projects, more than five million lines in C, C++, Java, PHP and Python, and reports 493 issues. Claude inventoried over 17,000 configuration options, 3,842 of them security relevant. It found 162 security-sensitive option combinations that were accepted with no warning and no documentation of their interaction; in 94 of them the combination silently turned off a security control. In the 11 "gated" projects, which are meant to serve only authenticated users, it reports 93 unnecessary pre-authentication surfaces. The post says none of these would have been immediately exploitable on its own.

The OpenSSH case is the concrete one. In the 10.4 release, Claude traced about 4,500 lines of experimental ML-DSA-44 code that an unauthenticated client could reach in the default configuration, roughly 16% of sshd's pre-authentication code, even when an administrator had excluded the algorithm. Anthropic sent patches; version 10.5 moved the check earlier, Claude then found two gaps in that check, and the maintainers shipped a further fix in 10.6.

Anthropic packaged the method as a Claude skill that runs three passes, each starting with an empty context window plus a short note from the prior pass. Every finding is confirmed with a dynamic trace. A proposed gate must leave default behavior unchanged, checked by running the project's own test suite and a black-box regression suite against the baseline, and any gate that would change a non-default configuration is set aside for a human to decide. The post gives counts of issues Claude reported, not how many maintainers confirmed outside the OpenSSH work, and the study comes from the lab that makes the model.

Why it matters: For anyone building an agent that edits code it did not write, the workflow is the reusable part: fresh-context passes, a runtime check on every claim, a hard "behavior must not change" test gate, and a named class of change reserved for a human. That is a verification loop you can copy before you copy the security topic.