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MEDIUM severity

CVE-2026-128122 — @sveltejs/adapter-cloudfl…

MEDIUMFix: sveltejs/kit@0a2e58c

CVE-2026-128122 is a medium-severity (CVSS 5.9) Cross-site Scripting (XSS) vulnerability in @sveltejs/adapter-cloudflare. A fix is available for @sveltejs/adapter-cloudflare — see the affected versions and patch details below.

SvelteKit: Prerendered redirect paths can inject arbitrary rules into the `_redirects` file generated by `@sveltejs/adapter-cloudflare`

Also known asGHSA-5wg4-q3ww-283h
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 14, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs35th percentile — riskier than 35% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

10other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
@sveltejs/adapter-cloudflarenpm
620Kdownloads / week

Description

SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. From version 4.7.0 until versions 7.2.10 and 8.0.2, @sveltejs/adapter-cloudflare allowed an attacker-influenced link crawled during prerendering to place whitespace, control characters, wildcards, or placeholders into a prerendered redirect path. The adapter wrote those paths into the Cloudflare _redirects output without output-context validation, allowing a path to create unintended routing rules that could redirect or expose requests beyond the intended prerendered route. This issue is fixed in 7.2.10 and 8.0.2.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
📦npm@sveltejs/adapter-cloudflare≥ 4.7.0&&< 7.2.107.2.10npm install @sveltejs/adapter-cloudflare@7.2.10
📦npm@sveltejs/adapter-cloudflare≥ 8.0.0-next.0&&< 8.0.28.0.2npm install @sveltejs/adapter-cloudflare@8.0.2

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @sveltejs/adapter-cloudflare, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update @sveltejs/adapter-cloudflare to 7.2.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-128122 is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. From version 4.7.0 until versions 7.2.10 and 8.0.2, @sveltejs/adapter-cloudflare allowed an attacker-influenced link crawled during prerendering to place whitespace, control characters, wildcards, or placeholders into a prerendered redirect path. The adapter wrote those paths into the Cloudflare _redirects output without output-context validation, allowing a path to create unintended routing rules that could redirect or expose requests beyond the intended prerendered route. This issue is fixed in
O3 Security · Impact-Aware SCA

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CVE-2026-128122: @sveltejs/adapter — Fixed in 7.2.10