Summary
opennextjs-cloudflare has SSRF vulnerability via /cdn-cgi/ path normalization bypass
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.
Credits
Disclosed responsibly by security researcher @Ezzer17.
Mitigations
The following mitigations have been put in place:
Server-side updates to Cloudflare's Workers platform to block backslash path normalization bypasses for /cdn-cgi requests. The update automatically mitigates the issue for all existing and any future sites deployed to Cloudflare Workers.
In addition to the platform level fix, Root cause fix has been implemented to the Cloudflare adapter for Open Next. The patched version of the adapter is found at @opennextjs/[email protected] (https://www.npmjs.com/package/@opennextjs/cloudflare)
Dependency update to the Next.js template used with create-cloudflare (c3) to use the fixed version of the Cloudflare adapter for Open Next. Despite the automatic mitigation deployed on Cloudflare's platform, we encourage affected users to upgrade to the patched version of @opennextjs/cloudflare.
Impact
- SSRF via path normalization bypass of Cloudflare edge interception
- Arbitrary remote content loading under the victim site's domain
- Same-origin policy bypass
- Potential for infrastructure abuse (scanning from Cloudflare IP space, worker resource exhaustion)
- Exposure of private assets stored under /cdn-cgi/ paths. For example, Open Next projects store incremental cache data under /cdn-cgi/_next_cache, which could be exposed via this bypass.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-3125? CVE-2026-3125 is a high-severity server-side request forgery (SSRF) vulnerability in @opennextjs/cloudflare (npm), affecting versions < 1.17.1. It is fixed in 1.17.1. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- Which versions of @opennextjs/cloudflare are affected by CVE-2026-3125? @opennextjs/cloudflare (npm) versions < 1.17.1 is affected.
- Is there a fix for CVE-2026-3125? Yes. CVE-2026-3125 is fixed in 1.17.1. Upgrade to this version or later.
- Is CVE-2026-3125 exploitable, and should I be worried? Whether CVE-2026-3125 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-3125 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-3125? Upgrade
@opennextjs/cloudflareto 1.17.1 or later.