CVE-2026-42567
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedSvelte is a performance oriented web framework. From version 5.51.5 to before version 5.55.7, an internal regex in the Svelte runtime can take exponential time to test in <svelte:element this={tag}></svelte:element>. This issue has been patched in version 5.55.7.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceSvelte versions 5.51.5 through 5.55.6 contain a ReDoS (Regular Expression Denial of Service) vulnerability in an internal regex used when processing `<svelte:element this={tag}></svelte:element>`. The regex exhibits exponential backtracking behavior with certain input patterns, allowing attackers to cause denial of service via crafted tag values.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 5.51.5, < 5.55.7CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Svelte versionRun 'npm list svelte' or inspect the version field in your package.json fileAffected if The installed version is >= 5.51.5 and < 5.55.7
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Identify svelte:element usageSearch your codebase for '<svelte:element' tags, specifically looking for the 'this' attributeAffected if Your code contains <svelte:element> tags with a 'this' attribute set
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Check if this attribute is dynamicExamine whether the 'this' attribute value is a variable or expression rather than a static string literalAffected if The 'this' attribute uses a variable, prop, or any expression that could change at runtime
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Assess input source for this attributeTrace the source of the value passed to the 'this' attribute - check if it comes from user input, URL parameters, APIs, or other untrusted sourcesAffected if The value passed to the 'this' attribute is derived from untrusted or user-controlled input such as query parameters, user data, or external APIs
You are affected if you are running Svelte version 5.51.5 or higher but below 5.55.7 AND your application uses <svelte:element> with a dynamic 'this' attribute that could receive specially crafted input patterns.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped5.55.7
Upgrade Svelte to version 5.55.7 or later to apply the patch. Review any user-controlled input passed to the `this` prop of `<svelte:element>` as a defense-in-depth measure.
Svelte 5.55.7
- Upgrade Svelte to version 5.55.7 or later
- Run your package manager update command: npm install [email protected] (or yarn add [email protected] / pnpm add [email protected])
- Rebuild and test your application to verify the fix is applied and no regressions occur
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,616.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-42567 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-42567 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data