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CVE-2026-35515

MEDIUMCVSS 6.3/10EPSS 0.23%

Last modified

CVE-2026-35515 is a medium-severity vulnerability rated 6.3/10 on the CVSS scale. 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). EPSS estimates a 0.23% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
6.1/10

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

CVSS 4.0
6.3/10

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability
0.23%

14.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
NestjsNest< 11.1.18

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-35515?
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.
How severe is CVE-2026-35515?
CVE-2026-35515 has a CVSS score of 6.3/10 (MEDIUM severity). The EPSS model estimates a 0.23% probability of exploitation in the next 30 days.
How do I fix CVE-2026-35515?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-35515?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST