CVE-2026-42567
Svelte: ReDoS in `<svelte:element>` Tag Validation
Svelte 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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- High
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
Svelte: ReDoS in `<svelte:element>` Tag Validation
Svelte 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.
- Record
CVE-2026-42567- CVSS 4.0
- 5.9 Medium
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N - Weakness
- CWE-1333
- Updated
- 2026-11-02
EUVDEUVD-2026-35702
Svelte 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.
- Record
EUVD-2026-35702- CVSS 4.0
- 5.9 Medium
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-9rmh-mm8f-r9h6
Svelte: ReDoS in `<svelte:element>` Tag Validation
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.
- Record
GHSA-9rmh-mm8f-r9h6- CVSS 4.0
- 5.9 Medium
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N - Weakness
- CWE-1333
- Updated
- 2026-11-02
NVD
Svelte 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.
- Record
CVE-2026-42567- CVSS 4.0
- 5.9 Medium
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Weakness
- CWE-1333
- Updated
- 2026-11-02
OSV
Svelte: ReDoS in `<svelte:element>` Tag Validation
Svelte 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.
- Record
CVE-2026-42567- CVSS 4.0
- 5.9 Medium
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N - Weakness
- CWE-1333
- Updated
- 2026-11-02
OSVGHSA-9rmh-mm8f-r9h6
Svelte: ReDoS in `<svelte:element>` Tag Validation
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.
- Record
GHSA-9rmh-mm8f-r9h6- CVSS 4.0
- 5.9 Medium
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N - Weakness
- CWE-1333
- Updated
- 2026-11-02
Affected products
Affected packages
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-42567 is a medium vulnerability (CVSS 5.9) in Svelte, published May 14, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.45%, the 39th percentile. Fixed in svelte 5.55.7.
References
github.com/sveltejs/svelte/security/advisories/GHSA-9rmh-mm8f-r9h6
nvd.nist.gov/vuln/detail/CVE-2026-42567