How severe is CVE-2026-42599?

CVE-2026-42599 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-42599 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-42599?

CVE-2026-42599 affects Svelte. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-42599?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-42599 have an EU (EUVD) identifier?

Yes. CVE-2026-42599 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-35703.

When was CVE-2026-42599 published?

CVE-2026-42599 was published on 2026-06-09 and last updated on 2026-06-17.

CVE-2026-42599

CVE-2026-42599 is a medium-severity vulnerability in Svelte with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.1)
CVSS v4: 5.1
EPSS exploit prediction: 0% (6th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-35703
Weakness: CWE-79
Affected product: Svelte
Published: 2026-06-09
Last modified: 2026-06-17

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.

Frequently asked questions

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.
How severe is CVE-2026-42599?: CVE-2026-42599 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-42599 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-42599?: CVE-2026-42599 affects Svelte. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-42599?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-42599 have an EU (EUVD) identifier?: Yes. CVE-2026-42599 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-35703.
When was CVE-2026-42599 published?: CVE-2026-42599 was published on 2026-06-09 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:svelte:svelte:*:*:*:*:*:node.js:*:*

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