blog: May 2026 security releases

Author: UlisesGascon

_posts/2026-05-31-security-releases.md

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+---
+title: May 2026 Security Releases
+description: Security releases for multiparty have been published. We recommend that all users upgrade as soon as possible.
+tags: security vulnerabilities
+authors:
+  - name: Ulises Gascon
+    github: UlisesGascon
+---
+
+The Express team has released [multiparty](https://www.npmjs.com/package/multiparty) 4.3.0, addressing three denial of service vulnerabilities in the multipart form parser.
+
+{% include admonitions/warning.html
+content="We recommend upgrading to the latest version of multiparty to secure your applications."
+%}
+
+The following vulnerabilities have been addressed:
+
+- [CVE-2026-8159 in multiparty utility module (High)](#cve-2026-8159-in-multiparty-utility-module-high)
+- [CVE-2026-8161 in multiparty utility module (High)](#cve-2026-8161-in-multiparty-utility-module-high)
+- [CVE-2026-8162 in multiparty utility module (High)](#cve-2026-8162-in-multiparty-utility-module-high)
+
+## CVE-2026-8159 in multiparty utility module (High)
+
+**[multiparty](https://www.npmjs.com/package/multiparty) versions `<= 4.2.3` are vulnerable to regular expression denial of service via filename parsing**
+
+A crafted multipart upload with a long header value can cause regex matching in the Content-Disposition filename parser to take seconds, blocking the Node.js event loop. Any service accepting multipart uploads via multiparty is affected. A small header of around 8 KB is sufficient to trigger the vulnerable backtracking.
+
+**Affected versions**: `<= 4.2.3`
+**Patched version**: `>= 4.3.0`
+
+For more details, see [GHSA-65x3-rw7q-gx94](https://github.com/pillarjs/multiparty/security/advisories/GHSA-65x3-rw7q-gx94).
+
+## CVE-2026-8161 in multiparty utility module (High)
+
+**[multiparty](https://www.npmjs.com/package/multiparty) versions `<= 4.2.3` are vulnerable to denial of service via prototype pollution leading to an uncaught exception**
+
+A multipart upload with a field name that collides with an inherited Object.prototype property such as `__proto__`, `constructor`, or `toString` causes the parser to invoke `.push()` on the inherited prototype value rather than an array, throwing a TypeError that propagates as an uncaught exception and crashes the process. Any service accepting multipart uploads via multiparty is affected.
+
+**Affected versions**: `<= 4.2.3`
+**Patched version**: `>= 4.3.0`
+
+For more details, see [GHSA-qxch-whhj-8956](https://github.com/pillarjs/multiparty/security/advisories/GHSA-qxch-whhj-8956).
+
+## CVE-2026-8162 in multiparty utility module (High)
+
+**[multiparty](https://www.npmjs.com/package/multiparty) versions `<= 4.2.3` are vulnerable to denial of service via an uncaught exception in filename* parameter parsing**
+
+A multipart upload with a Content-Disposition header whose `filename*` parameter contains a malformed percent-encoding causes the parser to invoke `decodeURI` on the value without try/catch. The resulting URIError propagates as an uncaught exception and crashes the process. Any service accepting multipart uploads via multiparty is affected.
+
+**Affected versions**: `<= 4.2.3`
+**Patched version**: `>= 4.3.0`
+
+For more details, see [GHSA-xh3c-6gcq-g4rv](https://github.com/pillarjs/multiparty/security/advisories/GHSA-xh3c-6gcq-g4rv).
+
+---
+
+We recommend upgrading to the latest version of multiparty to secure your applications.