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

> An attacker can crash the application by sending a crafted multipart request that triggers a prototype pollution-induced uncaught exception.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 May 2026
- **Updated:** 12 May 2026
- **Also known as:** DEBIAN-CVE-2026-8161, GHSA-qxch-whhj-8956, ROOT-APP-NPM-CVE-2026-8161, UBUNTU-CVE-2026-8161

## What is CVE-2026-8161?

CVE-2026-8161 is a high-severity denial of service vulnerability in multiparty, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-248 (Uncaught Exception), CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-8161?

2 open source packages ship an affected version, including multiparty. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `multiparty` | npm | All versions | 4.3.0 |
| `multiparty` | npm | All versions | 4.3.0 |

Products: Pillarjs Multiparty.

## How do I fix CVE-2026-8161?

Upgrade multiparty to 4.3.0 or later.

## Is CVE-2026-8161 being exploited?

There is no known exploitation of CVE-2026-8161 in the wild and no public exploit code.

Public exploit code:

- Proof of concept of CVE-2026-8161 (Multiparty) (github_poc): https://github.com/Ser0n-ath/multiparty-CVE-2026-8161

## Other vulnerabilities in multiparty

- [CVE-2026-8159](https://insights.sbomify.com/CVE-2026-8159/): multiparty vulnerable to ReDoS via filename parsing (high 7.5)
- [CVE-2026-8162](https://insights.sbomify.com/CVE-2026-8162/): multiparty vulnerable to Denial of Service via Uncaught Exception in filename* parameter parsing (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-8161 and fix it if it is affected.

What it is: CVE-2026-8161 is a high-severity denial of service vulnerability in multiparty, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-8161 in the wild and no public exploit code.

Affected packages and fixed versions:
- multiparty (npm): affected all versions; fixed in 4.3.0
- multiparty (npm): affected all versions; fixed in 4.3.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-8161/ (Markdown: https://insights.sbomify.com/CVE-2026-8161/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8161
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8161
- OSV: https://osv.dev/vulnerability/CVE-2026-8161

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-8161/
Summaries are generated and may contain mistakes; the official description above is the record.