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NestApplication · Nestjs

CVE-2026-35515

MEDIUM · 6.1 CVSS v3.1 Published 2026-04-07
Fix available
A fix is available. Upgrade to 11.1.18 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In NestJS versions prior to 11.1.18, the SseStream._transform() method interpolates message.type and message.id directly into Server-Sent Events (SSE) protocol output without sanitizing newline characters. Since SSE treats \r and \n as field delimiters and \n\n as event boundaries, an attacker who can control these fields through upstream data sources can inject arbitrary SSE events, spoof event types, and corrupt client reconnection state.

MitigationUpgrade NestJS to version 11.1.18 or later, which includes sanitization of newline characters in SseStream._transform(). Until then, validate and sanitize all message.type and message.id values at upstream sources to remove or escape \r and \n characters.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
NestApplication
Affected:< 11.1.18

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed NestJS version
    Run 'npm list @nestjs/core' or 'npm list nest' in your project directory to see the installed version of NestJS
    Affected if The installed version is lower than 11.1.18
  2. Identify SseStream usage in codebase
    Search your codebase for imports of SseStream from @nestjs/platform-sse or usage of ServerSentEventsModule, and review files that instantiate or extend SseStream
    Affected if Your application uses SseStream to handle Server-Sent Events responses
  3. Verify message.type and message.id sources
    Locate code where SseStream._transform() is called or where message objects with 'type' and 'id' properties are passed to the SSE stream; trace these values back to their origin (user input, database, API, etc.)
    Affected if The message.type or message.id values come from untrusted or user-controlled sources without validation
  4. Inspect SSE event output for newlines
    Capture actual SSE responses from your endpoints and examine the raw output for any or characters within the 'id:' or 'type:' fields
    Affected if Raw SSE output contains unsanitized newline characters in event id or type fields
  5. Check for upstream sanitization
    Search for any input validation, sanitization, or escaping logic applied to SSE message.type or message.id values before they reach SseStream (look for regex replacements, character stripping, or validation functions)
    Affected if No sanitization logic exists for newlines in message.type or message.id before SSE output

You are affected if your NestJS version is below 11.1.18 AND your application uses SseStream with message.type or message.id values sourced from untrusted input without sanitizing newline characters.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 11.1.18 or later
Fixed in 11.1.18
Interim mitigation

Upgrade NestJS to version 11.1.18 or later, which includes sanitization of newline characters in SseStream._transform(). Until then, validate and sanitize all message.type and message.id values at upstream sources to remove or escape \r and \n characters.

Recommended fix Moderate confidence

NestJS framework to version 11.1.18

  1. 1. Check current Nest package version in your project by running: npm list @nestjs/core
  2. 2. Update the NestJS package to version 11.1.18 by running: npm install @nestjs/[email protected]
  3. 3. If using other NestJS packages, update them to compatible 11.x versions: npm install @nestjs/[email protected] @nestjs/[email protected]
  4. 4. Verify the installation was successful: npm list @nestjs/core
  5. 5. Run your test suite to ensure the upgrade does not break existing functionality
  6. 6. Rebuild and deploy your application
Caveat Major version upgrades in NestJS can include breaking changes; review the NestJS changelog between your current version and 11.1.18 before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Nest Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,696.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-35515 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data