CVE-2025-15265 — svelte
Fix: sveltejs/svelte@ef81048CVE-2025-15265 is a Cross-site Scripting (XSS) vulnerability in svelte. A fix is available for svelte — see the affected versions and patch details below.
Svelte 5.46.0 - Hydratable Key Script-Breakout XSS (SSR)
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-15265.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
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.
sveltenpmDescription
Summary
An XSS vulnerability exists in Svelte 5.46.0-2 resulting from improper escaping of hydratable keys. If these keys incorporate untrusted user input, arbitrary JavaScript can be injected into server-rendered HTML.
Details
When using the hydratable function, the first argument is used as a key to uniquely identify the data, such that the value is not regenerated in the browser.
This key is embedded into a <script> block in the server-rendered <head> without escaping unsafe characters. A malicious key can break out of the script context and inject arbitrary JavaScript into the HTML response.
Impact
This is a cross-site scripting vulnerability affecting applications that have the experimental.async flag enabled and use hydratable with keys incorporating untrusted user input.
- Impact: Arbitrary JS execution in the client’s browser.
- Exploitability: Remote, single-request if key is attacker-controlled.
- Typical Outcomes:
- Session/token theft
- DOM defacement
- CSRF bypass via injected JS
- Account takeover depending on cookie/session strategy
Affected applications should upgrade to a patched version immediately.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | svelte | ≥ 5.46.0&&< 5.46.4 | 5.46.4npm install svelte@5.46.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for svelte, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update svelte to 5.46.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-15265 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-15265 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-15265. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-15265 in your dependencies?
O3 Security finds CVE-2025-15265 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.