CVE-2026-35515 — @nestjs/core
Fix: nestjs/nest#16686CVE-2026-35515 is a CWE-74 vulnerability in @nestjs/core. A fix is available for @nestjs/core — see the affected versions and patch details below.
@nestjs/core Improperly Neutralizes Special Elements in Output Used by a Downstream Component ('Injection')
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-35515.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@nestjs/corenpmDescription
Impact
What kind of vulnerability is it? Who is impacted?
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. Spring Framework's own security patch (6e97587) validates these same fields (id, event) for the same reason.
Actual impact:
- Event spoofing: Attacker forges SSE events with arbitrary
event:types, causing client-sideEventSource.addEventListener()callbacks to fire for wrong event types. - Data injection: Attacker injects arbitrary
data:payloads, potentially triggering XSS if the client renders SSE data as HTML without sanitization. - Reconnection corruption: Attacker injects
id:fields, corrupting theLast-Event-IDheader on reconnection, causing the client to miss or replay events. - Attack precondition: Requires the developer to map user-influenced data to the
typeoridfields of SSE messages. Direct HTTP request input does not reach these fields without developer code bridging the gap.
Patches
Has the problem been patched? What versions should users upgrade to?
Patched in @nestjs/[email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @nestjs/core | all versions | 11.1.18npm install @nestjs/core@11.1.18 |
Affected Products
nestnestjsDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @nestjs/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @nestjs/core to 11.1.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-35515 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for CVE-2026-35515 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-35515 in your dependencies?
Find it across npm, including transitive dependencies.