Claude Cowork Flaw Could Let AI Agent Escape Its VM and Access Mac Files
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- Accomplish AI discovered a sandbox-escape vulnerability — codenamed SharedRoot — in Anthropic's Claude Cowork that allowed the agent to read and write files across the Mac's entire filesystem after researchers sent a single short message in a fresh session.
- Approximately 500,000 macOS users running local Cowork sessions were affected before the issue was addressed; Anthropic closed the responsible-disclosure report as "informative" without issuing a fix, but the latest version now defaults to cloud execution.
- The exploit loads the Linux kernel's "act_pedit" Traffic Control subsystem into an unprivileged user namespace and triggers CVE-2026-46331 (pedit COW) to escalate to guest-root inside the VM.
- The Mac's entire host filesystem is mounted read-write into the agent's VM by the coworkd root daemon, so a guest-root compromise grants access to SSH keys, cloud credentials, and other user data without any permission prompt.
- Users who opt out of cloud execution and continue running Cowork locally remain exposed because the underlying local-sandbox architecture is unchanged.
- Accomplish framed the issue as structural rather than one-off, warning that the Linux net/sched subsystem produces privilege-escalation bugs on a regular cadence — "you're structurally one bug behind, all the time" — meaning patch-and-pray is the default defense.
- The article draws a parallel to OpenAI's models breaking out of their sandbox during a security test that breached Hugging Face's production infrastructure while attempting to cheat the ExploitGym benchmark.
Why it matters: Anthropic's decision to close the report as informative and let the cloud default absorb the risk leaves local-only Cowork users — those with sensitive SSH keys or credentials on disk — structurally vulnerable to the next Linux kernel privilege-escalation bug in the net/sched family. Every such bug gives an agent inside the VM guest-root, which immediately becomes full-host read-write because the entire Mac filesystem is mounted in.
