CVE-2026-71430

## Description `WrappedRE2::Replace` builds the replacement result and hands it to V8 with `.ToLocalChecked()` **without checking for the empty `MaybeLocal`** that V8 returns when the string/buffer exceeds its maximum length: `lib/replace.cc` (v1.24.1): ```cpp // L553 — Buffer return path info.GetReturnValue().Set(Nan::CopyBuffer(result.data(), result.size()).ToLocalChecked()); // L556 — String return path info.GetReturnValue().Set(Nan::New(result).ToLocalChecked()); ``` When a global replace uses an output-amplifying template — `$'` (text after the match) or `` $` `` (text before the match) — the result grows to **O(input²)**. For an input of ~40,000+ identical single-char matches the result exceeds V8's `String::kMaxLength` (~536,870,888 chars on 64-bit). `Nan::New(result)` then returns an **empty `MaybeLocal`**, and the unchecked `.ToLocalChecked()` calls `v8::Utils::ReportApiFailure` → **`FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal`** → `abort()` (SIGABRT). This is an **uncatchable** crash: it is not a JavaScript exception, so a surrounding `try/catch` cannot stop it — the entire Node process (or worker) dies. **The built-in regex engine handles the identical case correctly** by throwing a *catchable* `RangeError: Invalid string length`. node-re2 diverges from that contract and aborts instead. ## Proof of concept ``` npm i re2 node poc.js ``` ```js const RE2 = require('re2'); // Built-in engine: same case -> CATCHABLE RangeError (correct) try { 'a'.repeat(50000).replace(/a/g, "$'"); } catch (e) { console.log('native:', e.constructor.name, e.message); } // RangeError: Invalid string length // re2: ABORTS the whole process (uncatchable; try/catch does not help) 'a'.repeat(50000).replace(new RE2('a', 'g'), "$'"); // -> FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal (process exits 134 / SIGABRT) ``` Observed (Node v24, clean `npm i re2` → [email protected]): native branch prints `RangeError: Invalid string length`; the re2 branch aborts with `FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal`, stack top `WrappedRE2::Replace`, process exit code **134**. Threshold matches the mechanism precisely: input of 30,000 chars completes; 40,000 aborts (30000²/2 ≈ 4.5e8 < 5.37e8 max; 40000²/2 ≈ 8e8 > max). `$&`/constant templates and non-global replaces do not amplify and do not crash. ## Impact A remote, unauthenticated denial of service against any service that runs `String.prototype.replace` / the re2 `[Symbol.replace]` path where either the **replacement template** (containing `$'` or `` $` ``) or the **input size** is attacker-influenced. Because the failure is a native `abort()`, it cannot be contained by `try/catch` or domains — one request takes down the whole process/worker. This is especially impactful for re2's core audience, who adopt it specifically to process untrusted patterns/inputs safely. ## Suggested fix Check the `MaybeLocal` before `ToLocalChecked` on both return paths (and the intermediate group-string builds), and throw a catchable `RangeError` to match the built-in engine: ```cpp auto maybe = Nan::New(result); if (maybe.IsEmpty()) { Nan::ThrowRangeError("Invalid string length"); return; } info.GetReturnValue().Set(maybe.ToLocalChecked()); ``` (Apply equivalently to the `Nan::CopyBuffer(...)` buffer path at L553 and to the per-group `Nan::New(data, size).ToLocalChecked()` sites used by the replacer-function path.) ## Resolution Resolved in `re2` `1.25.1`. `WrappedRE2::Replace` now checks the returned `MaybeLocal` on every result path and throws a catchable `RangeError: Invalid string length` (matching the built-in engine) instead of aborting the process with an uncatchable `SIGABRT`. No API changes --- upgrade to `re2` >= `1.25.1` via a plain `npm upgrade` to receive the fix.