Next.js may leak x-middleware-subrequest-id to external hosts

Description

Summary

In the process of remediating CVE-2025-29927, we looked at other possible exploits of Middleware. We independently verified this low severity vulnerability in parallel with two reports from independent researchers.

Learn more here.

Credit

Thank you to Jinseo Kim kjsman and RyotaK (GMO Flatt Security Inc.) with takumi-san.ai for the responsible disclosure. These researchers were awarded as part of our bug bounty program.

Basic information

Type
reviewed
Severity
low
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2025-04-02 22:35:37 UTC
Updated
2025-10-13 15:35:51 UTC
GitHub reviewed
2025-04-02 22:35:37 UTC
NVD published
2025-04-02

EPSS Score

Score Percentile
0.21% 42.55%

CVSS Scores

Base score Version Severity Vector
1.7 4.0
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:H)
Exploitation depends on constrained or hard-to-reproduce conditions.
Attack requirements (AT:P)
Additional preconditions must be present for exploitation.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:L)
Limited confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:N)
No availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.
Exploit maturity (threat) (E:U)
Unreported: no public PoC, no reported exploitation, and no known simplification tools.

Identifiers

CWEs

CWE id Name
CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

Credits

  • Ry0taK (reporter)
  • takumi-san-ai (finder)

Affected packages (4)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
npm next = 12.3.5 12.3.6
npm next = 13.5.9 13.5.10
npm next = 14.2.25 14.2.26
npm next = 15.2.3 15.2.4

References

cvelogic Threat Intelligence