VulnerabilityAnalyzed

CVE-2026-42599

If an application spreads user-controlled or external data as element attributes, an attacker can inject malicious event handlers that execute in victims' browsers.

MEDIUM 5.1EPSS 0.21%

Does this matter?

Lower severity and a low EPSS score (0.21%). Track it; it rarely justifies an emergency change on its own.

Description

Svelte is a performance oriented web framework. Prior to version 5.55.7, 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. Note that this vulnerability only triggers if the user's browser has JavaScript enabled but Svelte's hydration mechanism does not reach the vulnerable element before the event fires. This issue has been patched in version 5.55.7.

CVSS 4.0: 5.1 MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/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: 0.21% probability · 11th percentile
CISA KEV: Not listed
Weakness: CWE-79
Affected: svelte/svelte
Source: security-advisories@github.com

References

https://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7Release Notes
https://github.com/sveltejs/svelte/security/advisories/GHSA-pr6f-5x2q-rwfpVendor Advisory

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