CVE-2026-6733: Undici Undici Vulnerable To HTTP Response Vulnerability

LOW
Advisory Identifier: GHSA-35p6-xmwp-9g52
Share
CVSS 3.7
CWE-367
Published
Advisory Summary

CVE-2026-6733 is a LOW (CVSS 3.7) undici vulnerable to http response vulnerability (CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition) affecting Undici libraries in the npm ecosystem. The issue involves undici vulnerable to http response queue poisoning via keep-alive socket reuse. Remediation is available by upgrading affected packages to version 8.5.0, 7.28.0, 6.27.0.

CVE-2026-6733 at a Glance

CVE Identifier CVE-2026-6733
GHSA Identifier GHSA-35p6-xmwp-9g52
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
Affected Product Undici
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 3.7

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:N/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 None (C:N)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-6733

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: 8.5.0 
npm install undici@8.5.0
undici fixed: 7.28.0 
npm install undici@7.28.0
undici fixed: 6.27.0 
npm install undici@6.27.0
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-2026-6733, 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 8.5.0), 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-367: Time-of-check Time-of-use (TOCTOU) Race Condition, where the product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. 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 HTTP/1.1 client is vulnerable to response queue poisoning on reused keep-alive sockets. An attacker-controlled upstream server can inject an unsolicited HTTP/1.1 response onto an idle socket after a request completes. When the client dispatches the next request on that socket, it associates the injected response with the new request, causing responses to be delivered to the wrong requests. This requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse. ## Patches Upgrade to undici v6.27.0, v7.28.0 or v8.5.0. ## Workarounds Disable keep-alive connection reuse by setting `keepAliveTimeout: 0` on the Client or Pool.

CVE-2026-6733 Affected Undici Versions

3 component(s)
Fixed Versions:
8.5.07.28.06.27.0
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
≥ 8.0.0
< 8.5.0
8.5.0
undici
npm/undici
npm
≥ 7.0.0
< 7.28.0
7.28.0
undici
npm/undici
npm
< 6.27.0
6.27.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nodejs/undici/security/advisories/GHSA-35p6-xmwp-9g52
NVD — CVE-2026-6733 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6733
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/6ea54ef8c4051e95bb68c89d4a5c9274fe6fbb4b
hackerone.com/reports/3582376 WEB
https://hackerone.com/reports/3582376
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/v6.27.0
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v7.28.0
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v8.5.0

Frequently Asked Questions

What is CVE-2026-6733?
CVE-2026-6733 is a security vulnerability in Undici involving undici vulnerable to HTTP response queue poisoning via keep-alive socket reuse under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition.
Which Undici versions are affected?
Affected versions include releases prior to 8.5.0, 7.28.0, 6.27.0 across affected packages: undici.
What version fixes CVE-2026-6733?
Upgrading to 8.5.0, 7.28.0, 6.27.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is undici affected?
Yes, undici is affected in releases prior to 8.5.0, 7.28.0, 6.27.0. Upgrade your dependency to 8.5.0, 7.28.0, 6.27.0 or later.
What is the CVSS score of CVE-2026-6733?
CVE-2026-6733 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-6733?
CVE-2026-6733 is classified under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition (The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.).
How can I check npm dependencies for CVE-2026-6733?
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-35p6-xmwp-9g52",
  "modified" : "2026-08-05T21:48:38Z",
  "published" : "2026-06-19T14:19:13Z",
  "aliases" : [ "CVE-2026-6733" ],
  "summary" : "undici vulnerable to HTTP response queue poisoning via keep-alive socket reuse",
  "details" : "## Impact\n\nUndici's HTTP/1.1 client is vulnerable to response queue poisoning on reused keep-alive sockets. An attacker-controlled upstream server can inject an unsolicited HTTP/1.1 response onto an idle socket after a request completes. When the client dispatches the next request on that socket, it associates the injected response with the new request, causing responses to be delivered to the wrong requests.\n\nThis requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse.\n\n## Patches\n\nUpgrade to undici v6.27.0, v7.28.0 or v8.5.0.\n\n## Workarounds\n\nDisable keep-alive connection reuse by setting `keepAliveTimeout: 0` on the Client or Pool.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.27.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.0.0"
      }, {
        "fixed" : "7.28.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.5.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/security/advisories/GHSA-35p6-xmwp-9g52"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6733"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/6ea54ef8c4051e95bb68c89d4a5c9274fe6fbb4b"
  }, {
    "type" : "WEB",
    "url" : "https://hackerone.com/reports/3582376"
  }, {
    "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/v6.27.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v7.28.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v8.5.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-367" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T14:19:13Z",
    "nvd_published_at" : "2026-06-17T18:18:05Z"
  }
}