CVE-2026-29057: Next HTTP Request Smuggling Vulnerability

MODERATE
Advisory Identifier: GHSA-ggv3-7p47-pfv8
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CWE-444
Published
Advisory Summary

CVE-2026-29057 is a MODERATE http request smuggling vulnerability (CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')) affecting Next libraries in the npm ecosystem. The issue involves http request smuggling in rewrites. Remediation is available by upgrading affected packages to version 16.1.7, 15.5.13.

CVE-2026-29057 at a Glance

CVE Identifier CVE-2026-29057
GHSA Identifier GHSA-ggv3-7p47-pfv8
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Affected Product Next
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-29057

To remediate this vulnerability, upgrade all affected Next dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

next fixed: 16.1.7 
npm install next@16.1.7
next fixed: 15.5.13 
npm install next@15.5.13
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls next

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-29057, inspect your project dependencies using npm:

npm ls next

Analyze the terminal output to locate any version of Next in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 16.1.7), your application is affected.

Note: The npm ls next command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling'), where the product acts as an intermediary http agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed http requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. In Next, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## Summary When Next.js rewrites proxy traffic to an external backend, a crafted `DELETE`/`OPTIONS` request using `Transfer-Encoding: chunked` could trigger request boundary disagreement between the proxy and backend. This could allow request smuggling through rewritten routes. ## Impact An attacker could smuggle a second request to unintended backend routes (for example, internal/admin endpoints), bypassing assumptions that only the configured rewrite destination/path is reachable. This does not impact applications hosted on providers that handle rewrites at the CDN level, such as Vercel. ## Patches The vulnerability originated in an upstream library vendored by Next.js. It is fixed by updating that dependency’s behavior so `content-length: 0` is added only when both `content-length` and `transfer-encoding` are absent, and `transfer-encoding` is no longer removed in that code path. ## Workarounds If upgrade is not immediately possible: - Block chunked `DELETE`/`OPTIONS` requests on rewritten routes at your edge/proxy. - Enforce authentication/authorization on backend routes per our [security guidance](https://nextjs.org/docs/app/guides/data-security).

CVE-2026-29057 Affected Next Versions

2 component(s)
Fixed Versions:
16.1.715.5.13
Product / Package Ecosystem Affected Versions Fixed Version
next
npm/next
npm
≥ 16.0.0-beta.0
< 16.1.7
16.1.7
next
npm/next
npm
≥ 9.5.0
< 15.5.13
15.5.13

References

GitHub Advisory / Wiki ADVISORY
https://github.com/vercel/next.js/security/advisories/GHSA-ggv3-7p47-pfv8
NVD — CVE-2026-29057 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-29057
Security Fix Commit FIX COMMIT
https://github.com/vercel/next.js/commit/dc98c04f376c6a1df76ec3e0a2d07edf4abdabd6
Next Source Repository REPOSITORY
https://github.com/vercel/next.js
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v15.5.13
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v16.1.7

Frequently Asked Questions

What is CVE-2026-29057?
CVE-2026-29057 is a security vulnerability in Next involving HTTP request smuggling in rewrites under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling').
Which Next versions are affected?
Affected versions include releases prior to 16.1.7, 15.5.13 across affected packages: next.
What version fixes CVE-2026-29057?
Upgrading to 16.1.7, 15.5.13 (or the latest patched release for your respective branch) resolves the vulnerability.
Is next affected?
Yes, next is affected in releases prior to 16.1.7, 15.5.13. Upgrade your dependency to 16.1.7, 15.5.13 or later.
What CWE is associated with CVE-2026-29057?
CVE-2026-29057 is classified under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.).
How can I check npm dependencies for CVE-2026-29057?
Run the dependency tree command: 'npm ls next'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
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  "schema_version" : "1.4.0",
  "id" : "GHSA-ggv3-7p47-pfv8",
  "modified" : "2026-03-18T21:53:28Z",
  "published" : "2026-03-17T16:17:15Z",
  "aliases" : [ "CVE-2026-29057" ],
  "summary" : "Next.js: HTTP request smuggling in rewrites",
  "details" : "## Summary\nWhen Next.js rewrites proxy traffic to an external backend, a crafted `DELETE`/`OPTIONS` request using `Transfer-Encoding: chunked` could trigger request boundary disagreement between the proxy and backend. This could allow request smuggling through rewritten routes.\n\n## Impact\nAn attacker could smuggle a second request to unintended backend routes (for example, internal/admin endpoints), bypassing assumptions that only the configured rewrite destination/path is reachable. This does not impact applications hosted on providers that handle rewrites at the CDN level, such as Vercel. \n\n## Patches\nThe vulnerability originated in an upstream library vendored by Next.js. It is fixed by updating that dependency’s behavior so `content-length: 0` is added only when both `content-length` and `transfer-encoding` are absent, and `transfer-encoding` is no longer removed in that code path.\n\n## Workarounds\nIf upgrade is not immediately possible:\n- Block chunked `DELETE`/`OPTIONS` requests on rewritten routes at your edge/proxy.\n- Enforce authentication/authorization on backend routes per our [security guidance](https://nextjs.org/docs/app/guides/data-security).",
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}