6.1

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

Analyzed
AliasesGHSA-pr6f-5x2q-rwfpCGA-7rwh-m426-7gffCGA-8mgm-9fhj-r5mj
Published 09-06-2026Last modified 09-06-2026

Vulnerability summary

CVE-2026-42599 is a medium (CVSS 6.1) vulnerability in svelte. EPSS estimates a 0.21% chance of exploitation in the next 30 days, higher than 10.5% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 5.1, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
6.1/10
010
Medium · v3.1 (NVD)
EPSS score
0.21%
0%100%
Low · -0.03 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 09-06-2026
    PublishedVulnerability first disclosed.
  2. 09-06-2026
    Last modifiedVulnerability information updated.

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 metrics

5 scores · 4 sources · 2 versions

EPSS trend

Probability

0.21%

Chance of exploitation in the next 30 days

Percentile

11%

Versus all other CVEs

30-day change

Decrease -0.03 pp

From 0.24% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, administrative account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard3 products
  • langfuse-2-workerAll versions (No fix recorded)
  • langfuse-fips-2-workerAll versions (No fix recorded)
  • langfuse-fips-3.152-workerAll versions (No fix recorded)
Npm1 product
  • svelte< 5.55.7
Svelte1 product
Sveltejs1 product

4 vendors · 6 products

References

6 links