fix: address stack overflow and performance issues in brace expansion

dist/index.js

@@ -10247,6 +10247,26 @@ var EXPANSION_MAX = 100000
 // characters) so legitimate input is unaffected.
 var EXPANSION_MAX_LENGTH = 4000000
 
+// `expand` recurses once per level of brace *nesting* - both when expanding a
+// set's comma members and when re-wrapping a set whose body is a single part.
+// The CVE-2026-14257 fix made the *tail* iterative (recursion on `m.post`, one
+// level per chained group), which left nesting depth unbounded: about 3,100
+// levels of `{{{...a,b...}}}` - only ~6KB of input - exhausted the native stack
+// and crashed the process. `EXPANSION_MAX_DEPTH` bounds how deep the parser
+// will follow nesting. It sits far above any realistic pattern and well below
+// the depth at which the stack runs out.
+var EXPANSION_MAX_DEPTH = 1000
+
+// Bash keeps a quirk where a brace group followed by a comma set still expands
+// (`{a},b}`). The parser implements it by rewriting the string and restarting
+// the scan, absorbing one `}` per pass. `n` trailing braces therefore cost `n`
+// full passes over a string that itself grows by one `escClose` sentinel each
+// time - quadratic in `n`, with a ~26x constant from the sentinel's length.
+// 128KB of `'{a}' + '}'.repeat(n) + ',z}'` blocked the event loop for 27
+// seconds to produce two results. `EXPANSION_MAX_REWRITES` bounds how many
+// times the scan may restart. Real `{a},b}` input needs a handful.
+var EXPANSION_MAX_REWRITES = 1000
+
 function numeric(str) {
   return parseInt(str, 10) == str
     ? parseInt(str, 10)
@@ -10270,34 +10290,54 @@ function unescapeBraces(str) {
 }
 
 
+// Like `target.push(...items)` but doesn't overflow the stack
+function pushAll(target, items) {
+  for (var i = 0; i < items.length; i++) {
+    target.push(items[i]);
+  }
+}
+
 // Basically just str.split(","), but handling cases
 // where we have nested braced sections, which should be
 // treated as individual members, like {a,{b,c},d}
 function parseCommaParts(str) {
-  if (!str)
-    return [''];
-
   var parts = [];
-  var m = balanced('{', '}', str);
 
-  if (!m)
-    return str.split(',');
+  // Walk the brace groups iteratively. Recursing on `post` once per group let a
+  // chain of them exhaust the stack - the parsing-side counterpart to
+  // the `expand` overflow fixed for CVE-2026-14257, and not something `max` or
+  // `maxLength` can bound, since it happens before expansion.
+  //
+  // The part the next chunk continues
+  var carry = '';
 
-  var pre = m.pre;
-  var body = m.body;
-  var post = m.post;
-  var p = pre.split(',');
+  for (;;) {
+    var m = balanced('{', '}', str);
 
-  p[p.length-1] += '{' + body + '}';
-  var postParts = parseCommaParts(post);
-  if (post.length) {
-    p[p.length-1] += postParts.shift();
-    p.push.apply(p, postParts);
+    if (!m) {
+      var tail = str.split(',');
+      tail[0] = carry + tail[0];
+      pushAll(parts, tail);
+      return parts;
+    }
+
+    var pre = m.pre;
+    var body = m.body;
+    var post = m.post;
+    var p = pre.split(',');
+
+    p[0] = carry + p[0];
+    p[p.length-1] += '{' + body + '}';
+
+    if (!post.length) {
+      pushAll(parts, p);
+      return parts;
+    }
+
+    carry = p.pop();
+    pushAll(parts, p);
+    str = post;
   }
-
-  parts.push.apply(parts, p);
-
-  return parts;
 }
 
 function expandTop(str, options) {
@@ -10307,6 +10347,8 @@ function expandTop(str, options) {
   options = options || {};
   var max = options.max == null ? EXPANSION_MAX : options.max;
   var maxLength = options.maxLength == null ? EXPANSION_MAX_LENGTH : options.maxLength;
+  var maxDepth = options.maxDepth == null ? EXPANSION_MAX_DEPTH : options.maxDepth;
+  var maxRewrites = options.maxRewrites == null ? EXPANSION_MAX_REWRITES : options.maxRewrites;
 
   // I don't know why Bash 4.3 does this, but it does.
   // Anything starting with {} will have the first two bytes preserved
@@ -10318,7 +10360,7 @@ function expandTop(str, options) {
     str = '\\{\\}' + str.substr(2);
   }
 
-  return expand(escapeBraces(str), max, maxLength, true).map(unescapeBraces);
+  return expand(escapeBraces(str), max, maxLength, maxDepth, 0, maxRewrites, true).map(unescapeBraces);
 }
 
 function identity(e) {
@@ -10442,8 +10484,18 @@ function expand(
   str,
   max,
   maxLength,
+  maxDepth,
+  depth,
+  maxRewrites,
   isTop
 ) {
+  // Too deeply nested to keep following: treat the rest as literal, the same
+  // way a group that cannot expand is already handled. Truncating rather than
+  // throwing keeps expansion total, matching `max` and `maxLength`.
+  if (depth > maxDepth) {
+    return [str];
+  }
+
   // Consume the string's top-level brace groups left to right, threading a
   // running set of combined prefixes (`acc`). Expanding the tail iteratively -
   // rather than recursing on `m.post` once per group - keeps the native stack
@@ -10464,6 +10516,9 @@ function expand(
   // `accBase[a]` records how much of `acc[a]` predates the current run;
   // `combine` treats an expansion as empty when it adds nothing past that.
   var accBase = [0]
+  // How many times the `{a},b}` rewrite below has restarted the scan. Each pass
+  // re-reads the whole string, so leaving this unbounded is quadratic.
+  var rewrites = 0
   var dropEmpties = false
   var firstGroup = true
   var nextBase
@@ -10495,7 +10550,8 @@ function expand(
     var isOptions = m.body.indexOf(',') >= 0;
     if (!isSequence && !isOptions) {
       // {a},b}
-      if (m.post.match(/,(?!,).*\}/)) {
+      if (rewrites < maxRewrites && m.post.match(/,(?!,).*\}/)) {
+        rewrites++;
         str = m.pre + '{' + m.body + escClose + m.post;
         // The rewritten string is expanded as if it were a fresh top-level one,
         // so start a new empty-drop run: anchor the baseline at what `acc`
@@ -10534,7 +10590,7 @@ function expand(
       var n = parseCommaParts(m.body);
       if (n.length === 1 && n[0] !== undefined) {
         // x{{a,b}}y ==> x{a}y x{b}y
-        n = expand(n[0], max, maxLength, false).map(embrace);
+        n = expand(n[0], max, maxLength, maxDepth, depth + 1, maxRewrites, false).map(embrace);
         //XXX is this necessary? Can't seem to hit it in tests.
         /* c8 ignore start */
         if (n.length === 1) {
@@ -10573,7 +10629,7 @@ function expand(
       values = []
       var valuesLength = 0
       outer: for (var j = 0; j < n.length; j++) {
-        var expanded = expand(n[j], max, maxLength, false)
+        var expanded = expand(n[j], max, maxLength, maxDepth, depth + 1, maxRewrites, false)
         for (var k = 0; k < expanded.length; k++) {
           var v = expanded[k]
           if (dropsEmpties && !v) continue