How severe is CVE-2026-42567?

No CVSS score has been assigned to CVE-2026-42567 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-42567?

CVE-2026-42567 affects the following packages: svelte (npm). Ecosystems affected: npm.

How do I fix CVE-2026-42567?

Update svelte to 5.55.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42567 is resolved across your whole dependency graph.

How do I detect CVE-2026-42567 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for svelte, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-42567 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-42567 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-42567 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-42567?

CVE-2026-42567 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 39th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-42567?

CVE-2026-42567 is classified as CWE-1333 (CWE-1333). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-42567 published, and has it been updated?

CVE-2026-42567 was published on June 9, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-42567 — svelte

CVE-2026-42567 is a CWE-1333 vulnerability in svelte. A fix is available for svelte — see the affected versions and patch details below.

Svelte: ReDoS in `<svelte:element>` Tag Validation

Also known asGHSA-9rmh-mm8f-r9h6

Published

Jun 9, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42567.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs39th percentile — riskier than 39% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

2Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

sveltenpm

9.5Mdownloads / week

Description

An internal regex in the Svelte runtime can take exponential time to test in <svelte:element this={tag}></svelte:element>. You are only vulnerable to this if you allow tags of unconstrained length. If your application only allows a predetermined list of tags or trims their length before passing them to svelte:element, you are safe.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`svelte`	≥ 5.51.5&&< 5.55.7	5.55.7`npm install svelte@5.55.7`

Affected Products

1 product · 1 configurations

Application

sveltesvelte

≥ 5.51.5 && < 5.55.7

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for svelte, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update svelte to 5.55.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42567 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

A flaw was found in Svelte. An internal regex in the Svelte runtime can take exponential time when processing specially crafted input in `<svelte:element this={tag}>` elements, leading to a Regular Expression Denial of Service (ReDoS). Red Hat products that ship svelte (Podman Desktop, Konflux) use it as a UI…

Workaround published by Red Hat

Upgrade to Svelte 5.55.7 or later.

Source: Red Hat security advisory for CVE-2026-42567 (CC BY 4.0)

Frequently Asked Questions

An internal regex in the Svelte runtime can take exponential time to test in `<svelte:element this={tag}></svelte:element>`. You are only vulnerable to this if you allow tags of unconstrained length. If your application only allows a predetermined list of tags or trims their length before passing them to `svelte:element`, you are safe.