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CVE-2026-3125

SSRF vulnerability in opennextjs-cloudflare via /cdn-cgi/ path normalization bypass

High7.7EPSS 0.40%
Published
Updated
Reserved
Assigned by
cloudflare

Description

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.

Scores

CVSS scores of CVE-2026-3125, by who scored it
Scored byCVSSScoreVector
cloudflareCNA (assigner)4.0High7.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:H/SI:N/SA:N
NVDNVD · Analyzed4.0High7.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS (exploitation in 30 days)
0.40% · top 66% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: yes · Technical impact: partial
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The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.7.

Weakness

Affected products

Affected packages

From reviewed advisories of the GitHub Advisory Database.

What to do

Solution: 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.

Solution: In addition to the platform level fix, root cause fix https://github.com/opennextjs/opennextjs-cloudflare/pull/1147 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 https://www.npmjs.com/package/@opennextjs/cloudflare )

Solution: Dependency update https://github.com/opennextjs/opennextjs-cloudflare/pull/1150 to the Next.js template used with create-cloudflare (c3) to use the fixed version of the Cloudflare adapter for Open Next.

References (4)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .