next.js: Inconsistent Interpretation of HTTP Requests
CVE-2025-49826 is a high-severity inconsistent interpretation of HTTP requests vulnerability in next.js from Vercel, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected next.js versions: >= 15.0.4-canary.51, < 15.1.8. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.13% chance of exploitation within 30 days, higher than 67% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of next.js you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (github.com).
Official description
Next.js is a React framework for building full-stack web applications. From versions 15.0.4-canary.51 to before 15.1.8, a cache poisoning bug leading to a Denial of Service (DoS) condition was found in Next.js. This issue does not impact customers hosted on Vercel. Under certain conditions, this issue may allow a HTTP 204 response to be cached for static pages, leading to the 204 response being served to all users attempting to access the page. This issue has been addressed in version 15.1.8.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Inconsistent Interpretation of HTTP Requests
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 developers prevent this class of flaw
- Use a web server that employs a strict HTTP parsing procedure, such as Apache.
- Terminate the client session after each request.
More Inconsistent Interpretation of HTTP Requests vulnerabilities (CWE-444)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
Other vulnerabilities in next.js
- 8.2 High severity
- 9.0 Critical severity
- 8.2 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Inconsistent Interpretation of HTTP Requests vulnerabilities
- 7.5 High severity
- 9.1 Critical severity
- 9.1 Critical severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
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