# CVE-2026-40879: Nest: DoS via Recursive handleData in JsonSocket (TCP Transport)

> An attacker can cause a stack overflow and denial of service in Nest applications by sending crafted TCP frames with many small JSON messages.

- **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:** 21 Apr 2026
- **Updated:** 21 Apr 2026
- **Also known as:** GHSA-hpwf-8g29-85qm

## What is CVE-2026-40879?

CVE-2026-40879 is a high-severity denial of service vulnerability in nestjs nest, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Nest is a framework for building scalable Node.js server-side applications. Prior to 11.1.19, when an attacker sends many small, valid JSON messages in one TCP frame, handleData() recurses once per message; the buffer shrinks each call. maxBufferSize is never reached; call stack overflows instead. A ~47 KB payload is sufficient to trigger RangeError. This vulnerability is fixed in 11.1.19.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-40879?

2 open source packages ship an affected version, including @nestjs/microservices. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@nestjs/microservices` | npm | All versions | 11.1.19 |
| `@nestjs/microservices` | npm | All versions | 11.1.19 |

Products: Nestjs Nest.

## How do I fix CVE-2026-40879?

Upgrade @nestjs/microservices to 11.1.19 or later.

## Is CVE-2026-40879 being exploited?

There is no known exploitation of CVE-2026-40879 in the wild and no public exploit code.

## Other vulnerabilities in nestjs nest

- [CVE-2026-33011](https://insights.sbomify.com/CVE-2026-33011/): Nest Fastify HEAD Request Middleware Bypass (high 8.7)
- [CVE-2026-2293](https://insights.sbomify.com/CVE-2026-2293/): NestJS 11.1.13 - Lack of data validation allowing authentication/authorization bypass (high 8.2)
- [CVE-2025-69211](https://insights.sbomify.com/CVE-2025-69211/): Nest has a Fastify URL Encoding Middleware Bypass (TOCTOU) (medium 6.9)
- [CVE-2026-35515](https://insights.sbomify.com/CVE-2026-35515/): @nestjs/core Improperly Neutralizes Special Elements in Output Used by a Downstream Component ('Injection') (medium 6.3)
- [CVE-2024-29409](https://insights.sbomify.com/CVE-2024-29409/): nest allows a remote attacker to execute arbitrary code via the Content-Type header (medium 5.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40879 and fix it if it is affected.

What it is: CVE-2026-40879 is a high-severity denial of service vulnerability in nestjs nest, published on 21 Apr 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-2026-40879 in the wild and no public exploit code.

Affected packages and fixed versions:
- @nestjs/microservices (npm): affected all versions; fixed in 11.1.19
- @nestjs/microservices (npm): affected all versions; fixed in 11.1.19

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-2026-40879/ (Markdown: https://insights.sbomify.com/CVE-2026-40879/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40879
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40879
- OSV: https://osv.dev/vulnerability/CVE-2026-40879

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40879/
Summaries are generated and may contain mistakes; the official description above is the record.