Cross-site scripting via spread attributes in Svelte SSR
CVE-2026-42599

5.1MEDIUM

Key Information:

Vendor

Sveltejs

Status
Svelte
Vendor
CVE Published:
9 June 2026

What is CVE-2026-42599?

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.

Affected Version(s)

svelte < 5.55.7

References

https://github.com/sveltejs/svelte/security/advisories/GH...
x_refsource_CONFIRM
https://github.com/sveltejs/svelte/releases/tag/svelte%40...
x_refsource_MISC

CVSS V4

Score:
5.1
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
High
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.