---
title: "CVE-2026-55091: flat-to-nested - Prototype Pollution"
description: "flat-to-nested < 1.1.2 contains a prototype pollution caused by using attacker-controlled id and parent fields as keys in internal objects, letting attackers corrupt application logic or cause denial of service, exploit requires attacker-controlled input to convert()."
url: https://panop.io/threat-heartbeat/CVE-2026-55091/
---

# CVE-2026-55091 flat-to-nested - Prototype Pollution

flat-to-nested < 1.1.2 contains a prototype pollution caused by using attacker-controlled id and parent fields as keys in internal objects, letting attackers corrupt application logic or cause denial of service, exploit requires attacker-controlled input to convert().

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.50% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-55091)

## Details

Type

Prototype Pollution

Impact

Denial Of Service, Data Tampering

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Published

14 September 2026

Updated

15 October 2026

Weakness

[CWE-915](https://cwe.mitre.org/data/definitions/915.html)

## Vendor fix

Update to version 1.1.2 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-55091](https://nvd.nist.gov/vuln/detail/CVE-2026-55091)
- [https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f](https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f)
- [https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2](https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2)
- [https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4](https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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