# CVE-2026-35515: @nestjs/core Improperly Neutralizes Special Elements in Output Used by a Downstream Component ('Injection')


- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 7 Apr 2026
- **Updated:** 7 Apr 2026
- **Also known as:** GHSA-36xv-jgw5-4q75, ROOT-APP-NPM-CVE-2026-35515

## What is CVE-2026-35515?

CVE-2026-35515 is a medium-severity vulnerability in nestjs nest, published on 7 Apr 2026. 

### Official description

Nest is a framework for building scalable Node.js server-side applications. Prior to 11.1.18, SseStream._transform() interpolates message.type and message.id directly into Server-Sent Events text protocol output without sanitizing newline characters (\r, \n). Since the SSE protocol treats both \r and \n as field delimiters and \n\n as event boundaries, an attacker who can influence these fields through upstream data sources can inject arbitrary SSE events, spoof event types, and corrupt reconnection state. This vulnerability is fixed in 11.1.18.

Weakness: CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component)

## Which versions are affected by CVE-2026-35515?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@nestjs/core` | npm | All versions | 11.1.18 |
| `@nestjs/core` | npm | All versions | 11.1.18 |

Products: Nestjs Nest.

## How do I fix CVE-2026-35515?

Upgrade @nestjs/core to 11.1.18 or later.

## Is CVE-2026-35515 being exploited?

There is no known exploitation of CVE-2026-35515 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-2026-40879](https://insights.sbomify.com/CVE-2026-40879/): Nest: DoS via Recursive handleData in JsonSocket (TCP Transport) (high 7.5)
- [CVE-2025-69211](https://insights.sbomify.com/CVE-2025-69211/): Nest has a Fastify URL Encoding Middleware Bypass (TOCTOU) (medium 6.9)
- [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-2026-35515 and fix it if it is affected.

What it is: CVE-2026-35515 is a medium-severity vulnerability in nestjs nest, published on 7 Apr 2026. 
Exploitation: There is no known exploitation of CVE-2026-35515 in the wild and no public exploit code.

Affected packages and fixed versions:
- @nestjs/core (npm): affected all versions; fixed in 11.1.18
- @nestjs/core (npm): affected all versions; fixed in 11.1.18

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-2026-35515/ (Markdown: https://insights.sbomify.com/CVE-2026-35515/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-35515
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-35515
- OSV: https://osv.dev/vulnerability/CVE-2026-35515

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-35515/
Summaries are generated and may contain mistakes; the official description above is the record.