CVE-2026-84933: Undici Undici Vulnerable To Cross-user Cookie Vulnerability

MODERATE
Advisory Identifier: GHSA-2jfj-6hjv-fm6j
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CVSS 6.5
CWE-524 CWE-200
Published
Advisory Summary

CVE-2026-84933 is a MODERATE (CVSS 6.5) undici vulnerable to cross-user cookie vulnerability (CWE-524: Use of Cache Containing Sensitive Information) affecting Undici libraries in the npm ecosystem. The issue involves undici vulnerable to cross-user cookie disclosure via set-cookie caching in shared caches. Remediation is available by upgrading affected packages to version 7.29.1, 8.10.2.

CVE-2026-84933 at a Glance

CVE Identifier CVE-2026-84933
GHSA Identifier GHSA-2jfj-6hjv-fm6j
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-524: Use of Cache Containing Sensitive Information
Affected Product Undici
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-84933

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

undici fixed: 7.29.1 
npm install undici@7.29.1
undici fixed: 8.10.2 
npm install undici@8.10.2
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 undici

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-84933, inspect your project dependencies using npm:

npm ls undici

Analyze the terminal output to locate any version of Undici in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 7.29.1), your application is affected.

Note: The npm ls undici 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-524: Use of Cache Containing Sensitive Information, where the code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere. In Undici, 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

### Impact undici's `interceptors.cache()` does not handle `Set-Cookie` in the cache path. In shared-cache mode (`type: 'shared'`, the default), a cacheable response (for example `Cache-Control: public, max-age=...`) carrying a `Set-Cookie` header is stored, and the stored `Set-Cookie` is re-served to a later caller that hits the same cache key. This exposes one user's cookie to another caller and lets an untrusted upstream inject cookies into cached responses served to all subsequent callers, violating RFC 6265 section 7.2 (a shared cache must not store cookies). Applications using the shared cache interceptor against untrusted or multi-user upstreams are affected. Private caches (`type: 'private'`) are not affected. ### Patches Upgrade to `7.29.1` or `8.10.2`. In shared-cache mode, undici no longer stores or re-serves responses containing `Set-Cookie`, including previously cached entries and revalidation paths. ### Workarounds Use a private cache (`type: 'private'`) for per-user responses, or avoid caching responses that set cookies. Applications acting as shared caches should strip `Set-Cookie` from responses before caching.

CVE-2026-84933 Affected Undici Versions

2 component(s)
Fixed Versions:
7.29.18.10.2
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
≥ 7.0.0
< 7.29.1
7.29.1
undici
npm/undici
npm
≥ 8.0.0
< 8.10.2
8.10.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nodejs/undici/security/advisories/GHSA-2jfj-6hjv-fm6j
NVD — CVE-2026-84933 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84933
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/b6c5a00252c37da9dd2db9bead053bb843e1f988
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/cb75bbb34224a968b4ad80cab8b7aba5e0b3b28a
Undici Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Undici Source Repository REPOSITORY
https://github.com/nodejs/undici
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v7.29.1
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v8.10.2

Frequently Asked Questions

What is CVE-2026-84933?
CVE-2026-84933 is a security vulnerability in Undici involving undici vulnerable to cross-user cookie disclosure via Set-Cookie caching in shared caches under CWE-524: Use of Cache Containing Sensitive Information.
Which Undici versions are affected?
Affected versions include releases prior to 7.29.1, 8.10.2 across affected packages: undici.
What version fixes CVE-2026-84933?
Upgrading to 7.29.1, 8.10.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is undici affected?
Yes, undici is affected in releases prior to 7.29.1, 8.10.2. Upgrade your dependency to 7.29.1, 8.10.2 or later.
What is the CVSS score of CVE-2026-84933?
CVE-2026-84933 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N.
What CWE is associated with CVE-2026-84933?
CVE-2026-84933 is classified under CWE-524: Use of Cache Containing Sensitive Information (The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere.).
How can I check npm dependencies for CVE-2026-84933?
Run the dependency tree command: 'npm ls undici'. 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-2jfj-6hjv-fm6j",
  "modified" : "2026-09-29T18:19:58Z",
  "published" : "2026-09-29T18:19:58Z",
  "aliases" : [ "CVE-2026-84933" ],
  "summary" : "undici vulnerable to cross-user cookie disclosure via Set-Cookie caching in shared caches",
  "details" : "### Impact\n\nundici's `interceptors.cache()` does not handle `Set-Cookie` in the cache path. In shared-cache mode (`type: 'shared'`, the default), a cacheable response (for example `Cache-Control: public, max-age=...`) carrying a `Set-Cookie` header is stored, and the stored `Set-Cookie` is re-served to a later caller that hits the same cache key. This exposes one user's cookie to another caller and lets an untrusted upstream inject cookies into cached responses served to all subsequent callers, violating RFC 6265 section 7.2 (a shared cache must not store cookies). Applications using the shared cache interceptor against untrusted or multi-user upstreams are affected. Private caches (`type: 'private'`) are not affected.\n\n### Patches\n\nUpgrade to `7.29.1` or `8.10.2`. In shared-cache mode, undici no longer stores or re-serves responses containing `Set-Cookie`, including previously cached entries and revalidation paths.\n\n### Workarounds\n\nUse a private cache (`type: 'private'`) for per-user responses, or avoid caching responses that set cookies. Applications acting as shared caches should strip `Set-Cookie` from responses before caching.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.0.0"
      }, {
        "fixed" : "7.29.1"
      } ]
    } ]
  }, {
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      "ecosystem" : "npm",
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    },
    "ranges" : [ {
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        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.10.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/security/advisories/GHSA-2jfj-6hjv-fm6j"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84933"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/b6c5a00252c37da9dd2db9bead053bb843e1f988"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/cb75bbb34224a968b4ad80cab8b7aba5e0b3b28a"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nodejs/undici"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v7.29.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v8.10.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200", "CWE-524" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T18:19:58Z",
    "nvd_published_at" : "2026-09-04T17:17:01Z"
  }
}