CVE-2026-42599: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in sveltejs svelte
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.
AI Analysis
Technical Summary
CVE-2026-42599 describes a cross-site scripting vulnerability in the Svelte web framework before version 5.55.7. When applications use spread syntax to render attributes from untrusted sources, event handler properties are included in the output HTML, enabling injection of malicious event handlers. This vulnerability triggers only if the victim's browser has JavaScript enabled and Svelte's hydration mechanism does not process the vulnerable element before the event fires. The vulnerability is addressed by a patch in Svelte version 5.55.7.
Potential Impact
An attacker can inject malicious event handlers into the HTML output of a Svelte application, potentially executing arbitrary JavaScript in the context of the victim's browser. This can lead to cross-site scripting attacks, compromising user data or session integrity. The vulnerability requires specific conditions related to JavaScript execution and hydration timing, which may limit exploitation scenarios.
Mitigation Recommendations
This vulnerability has been patched in Svelte version 5.55.7. Users and developers should upgrade to version 5.55.7 or later to remediate this issue. No additional mitigation steps are indicated by the vendor advisory.
CVE-2026-42599: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in sveltejs svelte
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 v4.0
Score 5.1medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-42599 describes a cross-site scripting vulnerability in the Svelte web framework before version 5.55.7. When applications use spread syntax to render attributes from untrusted sources, event handler properties are included in the output HTML, enabling injection of malicious event handlers. This vulnerability triggers only if the victim's browser has JavaScript enabled and Svelte's hydration mechanism does not process the vulnerable element before the event fires. The vulnerability is addressed by a patch in Svelte version 5.55.7.
Potential Impact
An attacker can inject malicious event handlers into the HTML output of a Svelte application, potentially executing arbitrary JavaScript in the context of the victim's browser. This can lead to cross-site scripting attacks, compromising user data or session integrity. The vulnerability requires specific conditions related to JavaScript execution and hydration timing, which may limit exploitation scenarios.
Mitigation Recommendations
This vulnerability has been patched in Svelte version 5.55.7. Users and developers should upgrade to version 5.55.7 or later to remediate this issue. No additional mitigation steps are indicated by the vendor advisory.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-29T00:31:15.725Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a284cbb8dd33fbd85664541
Added to database: 06/09/2026, 17:26:19 UTC
Last enriched: 06/09/2026, 23:26:41 UTC
Last updated: 07/31/2026, 19:22:58 UTC
Views: 32
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