CVE-2026-84890: Undici Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-3xpg-4rpp-hhhm
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CVSS 5.9
CWE-770
Published
Advisory Summary

CVE-2026-84890 is a MODERATE (CVSS 5.9) denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Undici libraries in the npm ecosystem. The issue involves undici vulnerable to denial of service via unbounded decompression of compressed responses. Remediation is available by upgrading affected packages to version 7.29.1, 8.10.2.

CVE-2026-84890 at a Glance

CVE Identifier CVE-2026-84890
GHSA Identifier GHSA-3xpg-4rpp-hhhm
Severity MODERATE
CVSS v3.1 Base Score 5.9
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Undici
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 5.9

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:N/A:H).

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 None (I:N)
Availability High (A:H)

How to Fix CVE-2026-84890

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-2026-84890, 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-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. 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 The `interceptors.decompress()` interceptor decompresses HTTP response bodies according to the untrusted `Content-Encoding` header. The number of decompression layers is capped at 5, but the total decompressed output size is not bounded and there is no option to limit it. A malicious or faulty upstream can return a small compressed payload (a compression bomb) that expands to hundreds of megabytes or gigabytes in client memory, exhausting memory and causing the Node.js process to crash or become unresponsive. Any application using the decompress interceptor to read responses from untrusted or compromised upstreams is affected. ### Patches Upgrade to `7.29.1` or `8.10.2`. The interceptor now accepts a `maxSize` option (default 64 MiB) and rejects responses whose decompressed output exceeds it with a `ResponseExceededMaxSizeError`. ### Workarounds Once upgraded, set a conservative `maxSize` on the interceptor. Before upgrading, avoid using `interceptors.decompress()` with untrusted upstreams, or apply a custom interceptor that enforces a decompressed output size limit.

CVE-2026-84890 Affected Undici Versions

2 component(s)
Fixed Versions:
7.29.18.10.2
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
≥ 7.15.0
< 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-3xpg-4rpp-hhhm
NVD — CVE-2026-84890 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84890
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/2c7d7e1227043c644c4c32cfd1e276f4fd4fcb11
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/7aac7f12f757844763c8b8f1ab6e305e80d55838
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-2026-84890?
CVE-2026-84890 is a security vulnerability in Undici involving undici vulnerable to Denial of Service via unbounded decompression of compressed responses under CWE-770: Allocation of Resources Without Limits or Throttling.
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-2026-84890?
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-2026-84890?
CVE-2026-84890 has a CVSS v3.1 base score of 5.9 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-84890?
CVE-2026-84890 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check npm dependencies for CVE-2026-84890?
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-3xpg-4rpp-hhhm",
  "modified" : "2026-09-29T18:20:37Z",
  "published" : "2026-09-29T18:20:37Z",
  "aliases" : [ "CVE-2026-84890" ],
  "summary" : "undici vulnerable to Denial of Service via unbounded decompression of compressed responses",
  "details" : "### Impact\n\nThe `interceptors.decompress()` interceptor decompresses HTTP response bodies according to the untrusted `Content-Encoding` header. The number of decompression layers is capped at 5, but the total decompressed output size is not bounded and there is no option to limit it. A malicious or faulty upstream can return a small compressed payload (a compression bomb) that expands to hundreds of megabytes or gigabytes in client memory, exhausting memory and causing the Node.js process to crash or become unresponsive. Any application using the decompress interceptor to read responses from untrusted or compromised upstreams is affected.\n\n### Patches\n\nUpgrade to `7.29.1` or `8.10.2`. The interceptor now accepts a `maxSize` option (default 64 MiB) and rejects responses whose decompressed output exceeds it with a `ResponseExceededMaxSizeError`.\n\n### Workarounds\n\nOnce upgraded, set a conservative `maxSize` on the interceptor. Before upgrading, avoid using `interceptors.decompress()` with untrusted upstreams, or apply a custom interceptor that enforces a decompressed output size limit.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.15.0"
      }, {
        "fixed" : "7.29.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.10.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/security/advisories/GHSA-3xpg-4rpp-hhhm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84890"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/2c7d7e1227043c644c4c32cfd1e276f4fd4fcb11"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/7aac7f12f757844763c8b8f1ab6e305e80d55838"
  }, {
    "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-770" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T18:20:37Z",
    "nvd_published_at" : "2026-09-04T18:18:01Z"
  }
}