CVE-2026-9277

Summary

shell-quote's quote() function did not validate object-token inputs against the operator model used by parse(). The .op field was backslash-escaped character by character using /(.)/g, which in JavaScript does not match line terminators (\n, \r, U+2028, U+2029). A line terminator in .op therefore passed through unescaped into the output; POSIX shells treat a literal \n as a command separator, so any content after it would execute as a second command.

The vulnerable code path is reachable in two ways. Neither requires the parser to misbehave — parse() only emits ops from a fixed control set — but both are documented API surface:

1. Direct construction. A caller builds { op: '...\n...' } from external input (e.g. a deserialized argument array) and passes it to quote().
2. envFn return. parse(cmd, envFn) is documented to splice the return value of envFn into the result array when it is an object. An attacker-influenced data source consulted by envFn can introduce an object token whose .op reaches quote().

Impact

Shell command injection in callers that pass object tokens with attacker-influenced .op values to quote() and then hand the result to a shell. The preconditions are narrower than ordinary string injection — they require the caller to feed object tokens into quote() — but object tokens are a public, documented part of the API surface, and quote() is intended to be a shell-safety boundary.

PoC

const { parse, quote } = require('shell-quote');

// Direct construction
quote([{ op: ';\nid' }]);
// → "\;\n\\i\\d"  ← literal newline; second line executes as a command

// Via parse() with an envFn returning attacker-shaped objects
const tokens = parse('echo $X', () => ({ op: ';\nid' }));
require('child_process').execSync(quote(tokens), { shell: true });
// Executes `id` after `echo \;`.