opennextjs cloudflare up to 1.17.0 /cdn-cgi/image/ server-side request forgery

Summaryinfo

A vulnerability was found in opennextjs cloudflare up to 1.17.0. It has been rated as critical. Impacted is an unknown function of the file /cdn-cgi/image/. This manipulation causes server-side request forgery. The identification of this vulnerability is CVE-2026-3125. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as critical was found in opennextjs cloudflare up to 1.17.0. Affected by this vulnerability is an unknown function of the file /cdn-cgi/image/. The manipulation with an unknown input leads to a server-side request forgery vulnerability. The CWE definition for the vulnerability is CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

A Server-Side Request Forgery (SSRF) vulnerability was identified in the @opennextjs/cloudflare package, resulting from a path normalization bypass in the /cdn-cgi/image/ handler.The @opennextjs/cloudflare worker template includes a /cdn-cgi/image/ handler intended for development use only. In production, Cloudflare's edge intercepts /cdn-cgi/image/ requests before they reach the Worker. However, by substituting a backslash for a forward slash (/cdn-cgi\image/ instead of /cdn-cgi/image/), an attacker can bypass edge interception and have the request reach the Worker directly. The JavaScript URL class then normalizes the backslash to a forward slash, causing the request to match the handler and trigger an unvalidated fetch of arbitrary remote URLs. For example: https://victim-site.com/cdn-cgi\image/aaaa/https://attacker.com In this example, attacker-controlled content from attacker.com is served through the victim site's domain (victim-site.com), violating the same-origin policy and potentially misleading users or other services. Note: This bypass only works via HTTP clients that preserve backslashes in paths (e.g., curl --path-as-is). Browsers normalize backslashes to forward slashes before sending requests. Additionally, Cloudflare Workers with Assets and Cloudflare Pages suffer from a similar vulnerability. Assets stored under /cdn-cgi/ paths are not publicly accessible under normal conditions. However, using the same backslash bypass (/cdn-cgi\... instead of /cdn-cgi/...), these assets become publicly accessible. This could be used to retrieve private data. For example, Open Next projects store incremental cache data under /cdn-cgi/_next_cache, which could be exposed via this bypass.

The weakness was shared by ez_z3r as GHSA-rvpw-p7vw-wj3m. It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-3125 since 02/24/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 1.17.1 eliminates this vulnerability. Applying a patch is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Cloud Software

Vendor

• opennextjs

Name

• cloudflare

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11
• 1.12
• 1.13
• 1.14
• 1.15
• 1.16
• 1.17.0

CPE 2.3info

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• 🔒
• 🔒

CPE 2.2info

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