Summary
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.
Impact
A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-42567? CVE-2026-42567 is a medium-severity inefficient regular expression (ReDoS) vulnerability in svelte (npm), affecting versions >= 5.51.5, <= 5.55.6. It is fixed in 5.55.7. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
- Which versions of svelte are affected by CVE-2026-42567? svelte (npm) versions >= 5.51.5, <= 5.55.6 is affected.
- Is there a fix for CVE-2026-42567? Yes. CVE-2026-42567 is fixed in 5.55.7. Upgrade to this version or later.
- Is CVE-2026-42567 exploitable, and should I be worried? Whether CVE-2026-42567 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-42567 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-42567? Upgrade
svelteto 5.55.7 or later.