---
title: "CVE-2026-59940: seroval: `seroval.fromJSON()` Promise resolver type confusion invokes attacker-controlled methods during deserialization"
url: https://erroneo.us/security/cve/CVE-2026-59940/
description: "CVE-2026-59940 (seroval (npm)): Seroval facilitates JS value stringification, including complex structures beyond JSON.stringify capabilities. Prior to…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-18
date_modified: 2026-08-18
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-59940"
kev: false
cvss: 9.8
epss: 0.00812
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-59940: seroval: `seroval.fromJSON()` Promise resolver type confusion invokes attacker-controlled methods during deserialization

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.8% , percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes seroval (npm) <= 1.5.2, fixed in 1.5.3 . Check your lockfile, including transitive dependencies.

## What it is

Seroval facilitates JS value stringification, including complex structures beyond JSON.stringify capabilities. Prior to 1.5.3, seroval.fromJSON() allows attacker-controlled JSON Promise control nodes to operate on values from the general deserialization reference table without verifying genuine internal Promise resolver records, causing deserialization side effects with plugins enabled and potentially unintended server-side invocation or remote code execution when downstream frameworks register callable wrappers. This issue is fixed in version 1.5.3.

## Affected packages

- npm `seroval` <= 1.5.2 → fixed: 1.5.3

## Affected products (CVE record)

- lxsmnsyc seroval: < 1.5.3

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.81% probability of exploitation activity in the next 30 days; percentile 56.

## Sources

- [GitHub Advisory GHSA-mv8w-475r-vwqw](https://github.com/advisories/GHSA-mv8w-475r-vwqw)
- [CVE.org record CVE-2026-59940](https://www.cve.org/CVERecord?id=CVE-2026-59940)
- [NVD entry CVE-2026-59940](https://nvd.nist.gov/vuln/detail/CVE-2026-59940)
- [github.com](https://github.com/lxsmnsyc/seroval/security/advisories/GHSA-mv8w-475r-vwqw)
- [npmjs.com](https://www.npmjs.com/package/seroval/v/1.5.3)

---
Source page: https://erroneo.us/security/cve/CVE-2026-59940/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt