CVE-2026-8159: Multiparty Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-65x3-rw7q-gx94
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CVSS 7.5
CWE-1333
Published
Advisory Summary

CVE-2026-8159 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-1333: Inefficient Regular Expression Complexity) affecting Multiparty libraries in the npm ecosystem. The issue involves multiparty vulnerable to redos via filename parsing. Remediation is available by upgrading affected packages to version 4.3.0.

CVE-2026-8159 at a Glance

CVE Identifier CVE-2026-8159
GHSA Identifier GHSA-65x3-rw7q-gx94
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-1333: Inefficient Regular Expression Complexity
Affected Product Multiparty
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-2026-8159

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

multiparty fixed: 4.3.0 
npm install multiparty@4.3.0
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 multiparty

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-8159, inspect your project dependencies using npm:

npm ls multiparty

Analyze the terminal output to locate any version of Multiparty in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.3.0), your application is affected.

Note: The npm ls multiparty 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-1333: Inefficient Regular Expression Complexity, where the product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential. In Multiparty, 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 multiparty@4.2.3 and lower versions are vulnerable to denial of service via regular expression backtracking in the `Content-Disposition` filename parameter parser. A multipart upload with a long header value containing `!filename="1` repeated can cause regex matching to take seconds, blocking the event loop. Any service accepting multipart uploads via multiparty is affected. ### Patches Users should upgrade to multiparty@4.3.0 or higher. ### Workarounds None. Limiting upload sizes at the proxy/gateway layer reduces but does not eliminate the attack surface, since a small ~8 KB header is sufficient to trigger the vulnerable backtracking. ### Resources - [OWASP: Regular expression Denial of Service (ReDoS)](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS)

CVE-2026-8159 Affected Multiparty Versions

1 component(s)
Fixed Versions:
4.3.0
Product / Package Ecosystem Affected Versions Fixed Version
multiparty
npm/multiparty
npm
< 4.3.0
4.3.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/pillarjs/multiparty/security/advisories/GHSA-65x3-rw7q-gx94
NVD — CVE-2026-8159 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-8159
Multiparty Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Multiparty Source Repository REPOSITORY
https://github.com/pillarjs/multiparty
Multiparty Release RELEASE
https://github.com/pillarjs/multiparty/releases/tag/v4.3.0
owasp.org/www-community/attac... WEB
https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS

Frequently Asked Questions

What is CVE-2026-8159?
CVE-2026-8159 is a security vulnerability in Multiparty involving multiparty vulnerable to ReDoS via filename parsing under CWE-1333: Inefficient Regular Expression Complexity.
Which Multiparty versions are affected?
Affected versions include releases prior to 4.3.0 across affected packages: multiparty.
What version fixes CVE-2026-8159?
Upgrading to 4.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is multiparty affected?
Yes, multiparty is affected in releases prior to 4.3.0. Upgrade your dependency to 4.3.0 or later.
What is the CVSS score of CVE-2026-8159?
CVE-2026-8159 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-2026-8159?
CVE-2026-8159 is classified under CWE-1333: Inefficient Regular Expression Complexity (The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.).
How can I check npm dependencies for CVE-2026-8159?
Run the dependency tree command: 'npm ls multiparty'. 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-65x3-rw7q-gx94",
  "modified" : "2026-05-18T17:40:10Z",
  "published" : "2026-05-18T17:40:10Z",
  "aliases" : [ "CVE-2026-8159" ],
  "summary" : "multiparty vulnerable to ReDoS via filename parsing",
  "details" : "### Impact\n\nmultiparty@4.2.3 and lower versions are vulnerable to denial of service via regular expression backtracking in the `Content-Disposition` filename parameter parser. A multipart upload with a long header value containing `!filename=\"1` repeated can cause regex matching to take seconds, blocking the event loop. Any service accepting multipart uploads via multiparty is affected.\n\n### Patches\n\nUsers should upgrade to multiparty@4.3.0 or higher.\n\n### Workarounds\n\nNone. Limiting upload sizes at the proxy/gateway layer reduces but does not eliminate the attack surface, since a small ~8 KB header is sufficient to trigger the vulnerable backtracking.\n\n### Resources\n\n- [OWASP: Regular expression Denial of Service (ReDoS)](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS)",
  "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" : "multiparty"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.3.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/pillarjs/multiparty/security/advisories/GHSA-65x3-rw7q-gx94"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-8159"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pillarjs/multiparty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pillarjs/multiparty/releases/tag/v4.3.0"
  }, {
    "type" : "WEB",
    "url" : "https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-18T17:40:10Z",
    "nvd_published_at" : "2026-05-12T10:16:48Z"
  }
}