CVE-2026-1525Network attack vector

Request smuggling via case-variant Content-Length duplicates

Published Mar 12, 2026 · Updated Mar 12, 2026

HTTP request smuggling in Node.js Undici before 6.24.0 and 7.0.0 through 7.23.0 allows remote attackers to send ambiguous requests. In lib/core/request.js, processHeader fails to reject another normalized Content-Length name after storing the first value, so case variants produce multiple lengths on the wire. Exploitation requires low-level APIs and user-controlled header names; inconsistent intermediary parsing enables ACL bypass or cache poisoning, while strict peers reject the request.

CVSS severity6.5
Medium
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Node.js Undici before 6.24.0 and 7.0.0 through 7.23.0 allows remote attackers to send ambiguous requests. In lib/core/request.js, processHeader fails to reject another normalized Content-Length name after storing the first value, so case variants produce multiple lengths on the wire. Exploitation requires low-level APIs and user-controlled header names; inconsistent intermediary parsing enables ACL bypass or cache poisoning, while strict peers reject the request.

The record

CVE
CVE-2026-1525
Published
Mar 12, 2026
Updated
Mar 12, 2026
Vendor
Node.js
Product
Undici
Classifications
CWE-444, CAPEC-33, CAPEC-273, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 12, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 12, 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=< 6.24.0; 7.0.0 < 7.24.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Node.js · Undiciversion=< 6.24.0; 7.0.0 < 7.24.0

Published CVSS scores

6.5OpenJS FoundationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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.

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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-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CAPEC-33HTTP Request Smuggling
CAPEC-273HTTP Response Smuggling
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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