CVE-2026-1526: Undici Undici Has Unbounded Memory Consumption Vulnerability

HIGH
Advisory Identifier: GHSA-vrm6-8vpv-qv8q
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CVSS 7.5
CWE-409
Published
Advisory Summary

CVE-2026-1526 is a HIGH (CVSS 7.5) undici has unbounded memory consumption vulnerability (CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)) affecting Undici libraries in the npm ecosystem. The issue involves undici has unbounded memory consumption in websocket permessage-deflate decompression. Remediation is available by upgrading affected packages to version 6.24.0, 7.24.0.

CVE-2026-1526 at a Glance

CVE Identifier CVE-2026-1526
GHSA Identifier GHSA-vrm6-8vpv-qv8q
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)
Affected Product Undici
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

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

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
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-2026-1526

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: 6.24.0 
npm install undici@6.24.0
undici fixed: 7.24.0 
npm install undici@7.24.0
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-2026-1526, 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 6.24.0), 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-409: Improper Handling of Highly Compressed Data (Data Amplification), where the product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. 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

## Description The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the `PerMessageDeflate.decompress()` method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold. ## Impact - Remote denial of service against any Node.js application using undici's WebSocket client - A single compressed WebSocket frame of ~6 MB can decompress to ~1 GB or more - Memory exhaustion occurs in native/external memory, bypassing V8 heap limits - No application-level mitigation is possible as decompression occurs before message delivery ### Patches Users should upgrade to fixed versions. ### Workarounds No workaround are possible.

CVE-2026-1526 Affected Undici Versions

2 component(s)
Fixed Versions:
6.24.07.24.0
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
< 6.24.0
6.24.0
undici
npm/undici
npm
≥ 7.0.0
< 7.24.0
7.24.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nodejs/undici/security/advisories/GHSA-vrm6-8vpv-qv8q
NVD — CVE-2026-1526 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-1526
hackerone.com/reports/3481206 WEB
https://hackerone.com/reports/3481206
Undici Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
datatracker.ietf.org/doc/html/rfc7692 WEB
https://datatracker.ietf.org/doc/html/rfc7692
Undici Source Repository REPOSITORY
https://github.com/nodejs/undici
owasp.org/www-community/attac... WEB
https://owasp.org/www-community/attacks/Denial_of_Service

Frequently Asked Questions

What is CVE-2026-1526?
CVE-2026-1526 is a security vulnerability in Undici involving Undici has Unbounded Memory Consumption in WebSocket permessage-deflate Decompression under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification).
Which Undici versions are affected?
Affected versions include releases prior to 6.24.0, 7.24.0 across affected packages: undici.
What version fixes CVE-2026-1526?
Upgrading to 6.24.0, 7.24.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is undici affected?
Yes, undici is affected in releases prior to 6.24.0, 7.24.0. Upgrade your dependency to 6.24.0, 7.24.0 or later.
What is the CVSS score of CVE-2026-1526?
CVE-2026-1526 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-1526?
CVE-2026-1526 is classified under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) (The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output.).
How can I check npm dependencies for CVE-2026-1526?
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-vrm6-8vpv-qv8q",
  "modified" : "2026-03-13T20:41:56Z",
  "published" : "2026-03-13T20:41:56Z",
  "aliases" : [ "CVE-2026-1526" ],
  "summary" : "Undici has Unbounded Memory Consumption in WebSocket permessage-deflate Decompression",
  "details" : "## Description\n\nThe undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a \"decompression bomb\") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive.\n\nThe vulnerability exists in the `PerMessageDeflate.decompress()` method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.\n\n## Impact\n\n- Remote denial of service against any Node.js application using undici's WebSocket client\n- A single compressed WebSocket frame of ~6 MB can decompress to ~1 GB or more\n- Memory exhaustion occurs in native/external memory, bypassing V8 heap limits\n- No application-level mitigation is possible as decompression occurs before message delivery\n\n### Patches\n\nUsers should upgrade to fixed versions.\n\n### Workarounds\n\nNo workaround are possible.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.24.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.0.0"
      }, {
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      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
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  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-1526"
  }, {
    "type" : "WEB",
    "url" : "https://hackerone.com/reports/3481206"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "WEB",
    "url" : "https://datatracker.ietf.org/doc/html/rfc7692"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nodejs/undici"
  }, {
    "type" : "WEB",
    "url" : "https://owasp.org/www-community/attacks/Denial_of_Service"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-409" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-13T20:41:56Z",
    "nvd_published_at" : "2026-03-12T21:16:23Z"
  }
}