CVE-2026-27118: @sveltejs/adapter vercel Remote Code Execution Vulnerability

MODERATE
Advisory Identifier: GHSA-9pq4-5hcf-288c
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CWE-346
Published
Advisory Summary

CVE-2026-27118 is a MODERATE remote code execution vulnerability (CWE-346: Origin Validation Error) affecting @sveltejs/adapter vercel libraries in the npm ecosystem. The issue involves cache poisoning in @sveltejs/adapter-vercel. Remediation is available by upgrading affected packages to version 6.3.2.

CVE-2026-27118 at a Glance

CVE Identifier CVE-2026-27118
GHSA Identifier GHSA-9pq4-5hcf-288c
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-346: Origin Validation Error
Affected Product @sveltejs/adapter vercel
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-27118

To remediate this vulnerability, upgrade all affected @sveltejs/adapter vercel dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@sveltejs/adapter-vercel fixed: 6.3.2 
npm install @sveltejs/adapter-vercel@6.3.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls @sveltejs/adapter-vercel

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-27118, inspect your project dependencies using npm:

npm ls @sveltejs/adapter-vercel

Analyze the terminal output to locate any version of @sveltejs/adapter vercel in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.3.2), your application is affected.

Note: The npm ls @sveltejs/adapter-vercel command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-346: Origin Validation Error, where the product does not properly verify that the source of data or communication is valid. In @sveltejs/adapter vercel, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-27118 Affected @sveltejs/adapter vercel Versions

1 component(s)
Fixed Versions:
6.3.2
Product / Package Ecosystem Affected Versions Fixed Version
@sveltejs/adapter-vercel
npm/@sveltejs/adapter-vercel
npm
< 6.3.2
6.3.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/sveltejs/kit/security/advisories/GHSA-9pq4-5hcf-288c
NVD — CVE-2026-27118 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27118
@sveltejs/adapter vercel Source Repository REPOSITORY
https://github.com/sveltejs/kit

Frequently Asked Questions

What is CVE-2026-27118?
CVE-2026-27118 is a security vulnerability in @sveltejs/adapter vercel involving Cache poisoning in @sveltejs/adapter-vercel under CWE-346: Origin Validation Error.
Which @sveltejs/adapter vercel versions are affected?
Affected versions include releases prior to 6.3.2 across affected packages: @sveltejs/adapter-vercel.
What version fixes CVE-2026-27118?
Upgrading to 6.3.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @sveltejs/adapter-vercel affected?
Yes, @sveltejs/adapter-vercel is affected in releases prior to 6.3.2. Upgrade your dependency to 6.3.2 or later.
What CWE is associated with CVE-2026-27118?
CVE-2026-27118 is classified under CWE-346: Origin Validation Error (The product does not properly verify that the source of data or communication is valid.).
How can I check npm dependencies for CVE-2026-27118?
Run the dependency tree command: 'npm ls @sveltejs/adapter-vercel'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9pq4-5hcf-288c",
  "modified" : "2026-02-23T22:21:38Z",
  "published" : "2026-02-19T15:18:02Z",
  "aliases" : [ "CVE-2026-27118" ],
  "summary" : "Cache poisoning in @sveltejs/adapter-vercel",
  "details" : "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.\n\nSuccessful exploitation requires a victim to visit an attacker-controlled link while authenticated.\n\nExisting deployments are protected by Vercel's WAF, but users should upgrade as soon as possible.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@sveltejs/adapter-vercel"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.3.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sveltejs/kit/security/advisories/GHSA-9pq4-5hcf-288c"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27118"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sveltejs/kit"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-346" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-19T15:18:02Z",
    "nvd_published_at" : "2026-02-20T22:16:29Z"
  }
}