Cross-Site Scripting (XSS) in svelte (CVE-2026-42599)
Summary
Cross-site scripting in svelte (CVE-2026-42599). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 5.55.7 or later.
Original description
The description as published by the source.
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 is similar to but different from CVE-2026-27121.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-42599 has been found in svelte.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade svelte to 5.55.7 or later.
If unsure, ask your IT team or search "svelte CVE-2026-42599" on the vendor's site.
CVE-2026-42599 (svelte) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Patched: 5.55.7 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in svelte.
Check the vendor advisory for the affected versions of svelte.
Severity: Medium (CVSS 6.1/10). Risk of unauthorized operations or information disclosure.
Update to 5.55.7.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'svelte' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'svelte' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
svelteを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade svelte to 5.55.7ステージング環境で 5.55.7 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- advisory nvd.nist.gov
- package github.com
- patch security-advisories@github.com
- web security-advisories@github.com
- web github.com