Command Injection via incomplete shell metacharacter blocklist in node:child_process (bypass of CVE-2026-27190 fix)

Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.7.0 to 2.7.1, A command injection vulnerability exists in Deno's node:child_process polyfill (shell: true mode) that bypasses the fix for CVE-2026-27190. The two-stage argument sanitization in transformDenoShellCommand (ext/node/polyfills/internal/child_process.ts) has a priority bug: when an argument contains a $VAR pattern, it is wrapped in double quotes (L1290) instead of single quotes. Double quotes in POSIX sh do not suppress backtick command substitution, allowing injected commands to execute. An attacker who controls arguments passed to spawnSync or spawn with shell: true can execute arbitrary OS commands, bypassing Deno's permission system. This vulnerability is fixed in 2.7.2.