CVE-2026-9277: Shell quote Shell-quote Quote() Does Not Escape Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-w7jw-789q-3m8p",
  "modified" : "2026-06-09T14:27:15Z",
  "published" : "2026-06-09T14:27:15Z",
  "aliases" : [ "CVE-2026-9277" ],
  "summary" : "shell-quote quote() does not escape newlines in object .op values",
  "details" : "### Summary\n\n`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.\n\nThe 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:\n\n1. **Direct construction.** A caller builds `{ op: '...\\n...' }` from external input (e.g. a deserialized argument array) and passes it to `quote()`.\n2. **`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()`.\n\n### Impact\n\nShell 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.\n\n### PoC\n\n```js\nconst { parse, quote } = require('shell-quote');\n\n// Direct construction\nquote([{ op: ';\\nid' }]);\n// → \"\\;\\n\\\\i\\\\d\"  ← literal newline; second line executes as a command\n\n// Via parse() with an envFn returning attacker-shaped objects\nconst tokens = parse('echo $X', () => ({ op: ';\\nid' }));\nrequire('child_process').execSync(quote(tokens), { shell: true });\n// Executes `id` after `echo \\;`.\n```\n\nConfirmed under `sh`, `bash`, `dash`, and `zsh`.\n\n### Patch\n\nFixed by replacing the per-character escape with strict shape validation in `quote()`. The object-token branch now:\n\n- **`{ op }`** — `.op` must be a string from the same allowlist the parser emits (`||`, `&&`, `;;`, `|&`, `<(`, `<<<`, `>>`, `>&`, `<&`, `&`, `;`, `(`, `)`, `|`, `<`, `>`). Anything else throws `TypeError`. This is the direct fix for the reported issue and removes the entire class of `.op` injection.\n- **`{ op: 'glob', pattern }`** — `.pattern` must be a string with no line terminators. Glob metacharacters (`*`, `?`, `[`, `]`, `{`, `}`, `,`) pass through; all other shell-special characters are backslash-escaped. (Previously the pattern field was discarded entirely and the literal string `\\g\\l\\o\\b` was emitted — a latent bug, not security-relevant.)\n- **`{ comment }`** — `.comment` must be a string with no line terminators (line terminators would end the shell comment and resume command parsing — same injection shape).\n- **Any other object shape** — `TypeError`.\n\nThe fix is allowlist-based rather than a targeted regex tweak, so it closes the reported vector and forecloses adjacent ones (U+2028 / U+2029 line separators in `.op`, line terminators in comments, unknown-shape objects coerced through `.replace`).\n\n### Workarounds\n\nPrior to upgrading, callers that build object tokens from untrusted input should validate `.op` against the parser's operator set themselves, and never construct `{ op }` from attacker-controlled strings.\n\n### Credits\n\nReported by Akshat Sinha",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "shell-quote"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.1.0"
      }, {
        "fixed" : "1.8.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.8.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ljharb/shell-quote/security/advisories/GHSA-w7jw-789q-3m8p"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-9277"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ljharb/shell-quote/commit/1518179"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ljharb/shell-quote"
  }, {
    "type" : "WEB",
    "url" : "https://www.npmjs.com/package/shell-quote"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2026/05/23/2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-77", "CWE-78" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-09T14:27:15Z",
    "nvd_published_at" : "2026-05-22T14:16:30Z"
  }
}