VulnerabilityAnalyzed

CVE-2026-27121

Versions of svelte prior to 5.51.5 are vulnerable to cross-site scripting (XSS) during server-side rendering.

MEDIUM 5.1EPSS 0.19%

Does this matter?

Lower severity and a low EPSS score (0.19%). Track it; it rarely justifies an emergency change on its own.

Description

svelte performance oriented web framework. Versions of svelte prior to 5.51.5 are vulnerable to cross-site scripting (XSS) during server-side rendering. When using spread syntax to render attributes from untrusted data, event handler properties are included in the rendered HTML output. If an application spreads user-controlled or external data as element attributes, an attacker can inject malicious event handlers that execute in victims' browsers. This vulnerability is fixed in 5.51.5.

CVSS 4.0: 5.1 MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
EPSS: 0.19% probability · 9th percentile
CISA KEV: Not listed
Weakness: CWE-79
Affected: svelte/svelte
Source: security-advisories@github.com

References

https://github.com/sveltejs/svelte/security/advisories/GHSA-f7gr-6p89-r883Vendor Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.