Vulnerability · Published Jan 15, 2026 · Assigned by Fluid Attacks

CVE-2025-15265Svelte 5.46.0 - Hydratable Key Script-Breakout XSS (SSR)

Medium 5.3

In plain English

A medium-severity cross-site scripting in Svelte from Svelte. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 28% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.3Medium

Exploit odds (30 days)0.3%top 71.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

An SSR XSS exists in async hydration when attacker‑controlled keys are passed to hydratable. The key is embedded inside a <script> block without HTML‑safe escaping, allowing </script> to terminate the script and inject arbitrary JavaScript. This enables remote script execution in users' browsers, with potential for session theft and account compromise. This issue affects Svelte: from 5.46.0 before 5.46.3.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	svelte	5.46.4	GHSA-6738-r8g5-qwp3

Affected products (as reported)

Vendor	Product	Versions
Svelte	Svelte	5.46.0 – before 5.46.3

Weakness: CWE-79 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

References

https://fluidattacks.com/advisories/lydian third-party-advisory
https://github.com/sveltejs/svelte/security/advisories/GHSA-6738-r8g5-qwp3 vendor-advisory