CVE-2026-29057Network attack vector

Backend route access via rewrite request smuggling

Published Mar 18, 2026 · Updated Mar 18, 2026

HTTP request smuggling in Next.js allows remote attackers to reach unintended backend routes through externally proxied rewrites. In affected releases from 9.5.0 before 15.5.13 and from 16.0.0-beta.0 before 16.1.7, the vendored http-proxy path adds content-length: 0 to chunked DELETE or OPTIONS requests and removes transfer-encoding, causing the backend to parse a different request boundary. Exploitation requires a self-hosted application with an external rewrite; it can expose internal or administrative routes, while CDN-level rewrites are unaffected.

CVSS severity6.3
Medium
EPSS probability0.43%
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 Next.js allows remote attackers to reach unintended backend routes through externally proxied rewrites. In affected releases from 9.5.0 before 15.5.13 and from 16.0.0-beta.0 before 16.1.7, the vendored http-proxy path adds content-length: 0 to chunked DELETE or OPTIONS requests and removes transfer-encoding, causing the backend to parse a different request boundary. Exploitation requires a self-hosted application with an external rewrite; it can expose internal or administrative routes, while CDN-level rewrites are unaffected.

The record

CVE
CVE-2026-29057
Published
Mar 18, 2026
Updated
Mar 18, 2026
Vendor
Vercel
Product
Next.js
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 18, 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=>= 16.0.0-beta.0, < 16.1.7
  2. Affected versionversion=>= 9.5.0, < 15.5.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Vercel · Next.jsversion=>= 16.0.0-beta.0, < 16.1.7; version=>= 9.5.0, < 15.5.13

Published CVSS scores

6.5NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
6.3GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

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

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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