Packages / next / Security

ModerateVulnerabilityGHSA-ggv3-7p47-pfv8CVE-2026-29057Published 17 Mar 2026

Next.js: HTTP request smuggling in rewrites

Affected releases · next

  • 16.x16.0.0 – 16.1.6Fixed in 16.1.7
  • 15.x15.0.0 – 15.5.12Fixed in 15.5.13
  • 14.x14.0.0 – 14.2.35No fix on this line yet
  • 13.x and older9.5.0 – 13.5.11No fix, no longer updated

On 16.x, the newest line:

npm install next@16.1.7
16.x

  1. Affected

    16.0.0 – 16.1.6

    19 releases

  2. Fixed

    16.1.7 – 16.4.2

    26 releases, latest

15.x

  1. Affected

    15.0.0 – 15.5.12

    67 releases

  2. Fixed

    15.5.13 – 15.5.28

    15 releases

14.x

  1. Affected

    14.0.0 – 14.2.35

    46 releases

13.x

  1. Affected

    13.0.0 – 13.5.11

    56 releases

12.x

  1. Affected

    12.0.0 – 12.3.7

    33 releases

11.x

  1. Affected

    11.0.0 – 11.1.4

    7 releases

10.x

  1. Affected

    10.0.0 – 10.2.3

    18 releases

9.x

  1. Not affected

    9.0.0 – 9.4.4

    32 releases

  2. Affected

    9.5.0 – 9.5.5

    6 releases

423 stable releases of next, oldest to newest, one row per major.

Is your project affected?

Paste your package.json, or type the range you declare for next. It is read in your browser and sent nowhere.

What happens

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.