CVE-2026-35515Network attack vector

Event spoofing via unsanitized SSE delimiters

Published Apr 7, 2026 · Updated Apr 7, 2026

Server-Sent Events injection in Nest before 11.1.18 allows attackers to spoof events and corrupt reconnection state via crafted message fields. SseStream._transform() writes message.type and message.id into SSE output without removing carriage returns or line feeds, which become protocol fields and event boundaries. Exploitation requires developer code to map attacker-controlled data into type or id; direct HTTP input does not reach those fields by default.

CVSS severity6.3
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Server-Sent Events injection in Nest before 11.1.18 allows attackers to spoof events and corrupt reconnection state via crafted message fields. SseStream._transform() writes message.type and message.id into SSE output without removing carriage returns or line feeds, which become protocol fields and event boundaries. Exploitation requires developer code to map attacker-controlled data into type or id; direct HTTP input does not reach those fields by default.

The record

CVE
CVE-2026-35515
Published
Apr 7, 2026
Updated
Apr 7, 2026
Vendor
NestJS
Product
Nest
Classifications
CWE-74, T1565.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 11.1.18

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NestJS · Nestversion=< 11.1.18

Published CVSS scores

6.3GitHub, Inc.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
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
T1565.002Transmitted Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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