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VulnerabilityPublished Updated

CVE-2026-27118: sveltejs kit · Origin Validation Error

Affects sveltejs kitSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium : upgrade to 6.3.2 when convenient.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 4.0 base score
5.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 19% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 6.3.2
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 20 Feb 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade sveltejs kit to 6.3.2.

Affected software

ProductAffectedFixed in
sveltejskitAffected
  • <6.3.2
Fixed in
  • 6.3.2

AI-suggested

To mitigate this vulnerability, organizations should immediately upgrade @sveltejs/adapter-vercel to version 6.3.2 or later, where the origin validation and cache poisoning issues are fixed. Review and audit caching configurations to ensure that user-specific or sensitive responses are not cached globally or shared across users. Implement strict validation of query parameters related to ISR to prevent unauthorized cache manipulation. Employ Content Security Policy (CSP) and other browser security headers to reduce the risk of malicious link exploitation. Educate users about phishing risks to minimize the chance of clicking attacker-controlled links while authenticated. For deployments on Vercel, verify that the WAF is enabled and properly configured to filter suspicious requests. Consider implementing additional application-layer protections such as user session binding to cached content or cache partitioning by user identity. Regularly monitor logs for unusual cache behavior or access patterns indicative of exploitation attempts. Finally, maintain an up-to-date inventory of SvelteKit versions in use and apply security patches promptly.

Description

SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Versions of @sveltejs/adapter-vercel prior to 6.3.2 are vulnerable to cache poisoning. An internal query parameter intended for Incremental Static Regeneration (ISR) is accessible on all routes, allowing an attacker to cause sensitive user-specific responses to be cached and served to other users. Successful exploitation requires a victim to visit an attacker-controlled link while authenticated. Existing deployments are protected by Vercel's WAF, but users should upgrade as soon as possible. This vulnerability is fixed in 6.3.2.

References

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