Claude Code Sandbox Flaw May Compromise User Secrets

A null-byte hostname injection in Anthropic's Claude Code sandbox (affecting versions 2.0.24–2.1.89, ~130 releases) allowed attackers to craft SOCKS5 hostnames that pass JavaScript validation but resolve to attacker-controlled domains, enabling full sandbox bypass and silent exfiltration of sensitive data (API keys, env vars, source code, cloud metadata). Anthropic released a fix in v2.1.90 on April 1, 2026 that adds stricter hostname validation, but no public advisory or CVE was published; users are advised to upgrade, audit outbound logs, and rotate credentials.