--- title: May 2026 Security Releases · Express.js | daily.dev description: Multiparty 4.3.0 has been released to fix three high-severity denial of service vulnerabilities in versions 4.2.3 and earlier. CVE-2026-8159 is a ReDoS in... canonical: https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: May 2026 Security Releases · Express.js | daily.dev og:description: Multiparty 4.3.0 has been released to fix three high-severity denial of service vulnerabilities in versions 4.2.3 and earlier. CVE-2026-8159 is a ReDoS in... og:url: https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f og:image: https://api.daily.dev/og/posts/KdS06Vt1F.png og:image:alt: May 2026 Security Releases · Express.js og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # May 2026 Security Releases · Express.js **[Express.js](https://daily.dev/sources/expressjs-blog)** · 2 min read · 0 upvotes · 0 comments ## Summary Multiparty 4.3.0 has been released to fix three high-severity denial of service vulnerabilities in versions 4.2.3 and earlier. CVE-2026-8159 is a ReDoS in Content-Disposition filename parsing triggerable with an ~8KB header. CVE-2026-8161 is a prototype pollution issue where a colliding field name like __proto__ crashes the process. CVE-2026-8162 is an uncaught URIError from malformed percent-encoding in the filename* parameter. All services accepting multipart uploads via multiparty are affected; upgrading to 4.3.0 or later is recommended. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What vulnerabilities does multiparty 4.3.0 fix? Multiparty 4.3.0 fixes three high-severity denial of service vulnerabilities affecting versions 4.2.3 and earlier. CVE-2026-8159 is a regular expression denial of service in Content-Disposition filename parsing, triggerable with roughly an 8 KB header. CVE-2026-8161 is a prototype pollution bug where a field name like __proto__ crashes the process. CVE-2026-8162 is an uncaught URIError from malformed percent-encoding in the filename* parameter. _Track dependency CVEs like these on daily.dev before they hit production multipart upload handling._ ### How can a field name like __proto__ crash a Node.js app using multiparty? In multiparty versions 4.2.3 and earlier, a multipart upload field name colliding with an inherited Object.prototype property such as __proto__, constructor, or toString causes the parser to call .push() on the inherited prototype value instead of an array. This throws a TypeError that propagates as an uncaught exception and crashes the process. Upgrading to 4.3.0 patches it. _daily.dev helps developers stay ahead of prototype pollution bugs across their dependency tree._ ### Is multiparty still safe to use for handling file uploads in Node.js? Multiparty is safe when running version 4.3.0 or later, which patches three high-severity denial of service issues found in 4.2.3 and earlier: a ReDoS in filename parsing, a prototype pollution crash, and an uncaught URIError from malformed percent-encoding in filename* parameters. Any service accepting multipart uploads on an older version remains exposed and should upgrade immediately. _Developers choosing upload libraries can weigh security track records like this one on daily.dev._ ## Similar posts on daily.dev - [September 2026 Security Releases · Express.js](https://daily.dev/posts/september-2026-security-releases-express-js-ivoho9puc) · Express.js · 1 upvotes · 0 comments - [July 2026 Security Releases · Express.js](https://daily.dev/posts/july-2026-security-releases-express-js-tcsj3rcgu) · Express.js · 1 upvotes · 1 comments - [August 2026 Security Releases · Express.js](https://daily.dev/posts/august-2026-security-releases-express-js-kdzxqxlti) · Express.js · 2 upvotes · 0 comments - [Next.js May 2026 security release](https://daily.dev/posts/next-js-may-2026-security-release-hmqrmcava) · Vercel · 131 upvotes · 4 comments --- Tags: [#cyber](https://daily.dev/tags/cyber), [#nodejs](https://daily.dev/tags/nodejs), [#npm](https://daily.dev/tags/npm) [View this post on daily.dev](https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"May 2026 Security Releases · Express.js","url":"https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f"},"datePublished":"2026-08-23T12:17:34.965Z","dateModified":"2026-08-23T12:22:39.824Z","description":"Multiparty 4.3.0 has been released to fix three high-severity denial of service vulnerabilities in versions 4.2.3 and earlier. CVE-2026-8159 is a ReDoS in...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/3e897961b9d2a91bd1a712915bb59377?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/3e897961b9d2a91bd1a712915bb59377?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Express.js","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Express.js","logo":"https://media.daily.dev/image/upload/s--NvBVN7aT--/f_auto,q_auto/v1787487436/logos/expressjs-blog?_a=BAMAMicg0","url":"https://daily.dev/sources/expressjs-blog"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"cyber,nodejs,npm","timeRequired":"PT2M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Express.js","item":"https://daily.dev/sources/expressjs-blog"},{"@type":"ListItem","position":3,"name":"May 2026 Security Releases · Express.js"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/may-2026-security-releases-express-js-kds06vt1f#faq","mainEntity":[{"@type":"Question","name":"What vulnerabilities does multiparty 4.3.0 fix?","acceptedAnswer":{"@type":"Answer","text":"Multiparty 4.3.0 fixes three high-severity denial of service vulnerabilities affecting versions 4.2.3 and earlier. CVE-2026-8159 is a regular expression denial of service in Content-Disposition filename parsing, triggerable with roughly an 8 KB header. CVE-2026-8161 is a prototype pollution bug where a field name like __proto__ crashes the process. CVE-2026-8162 is an uncaught URIError from malformed percent-encoding in the filename* parameter. Track dependency CVEs like these on daily.dev before they hit production multipart upload handling."}},{"@type":"Question","name":"How can a field name like __proto__ crash a Node.js app using multiparty?","acceptedAnswer":{"@type":"Answer","text":"In multiparty versions 4.2.3 and earlier, a multipart upload field name colliding with an inherited Object.prototype property such as __proto__, constructor, or toString causes the parser to call .push() on the inherited prototype value instead of an array. This throws a TypeError that propagates as an uncaught exception and crashes the process. Upgrading to 4.3.0 patches it. daily.dev helps developers stay ahead of prototype pollution bugs across their dependency tree."}},{"@type":"Question","name":"Is multiparty still safe to use for handling file uploads in Node.js?","acceptedAnswer":{"@type":"Answer","text":"Multiparty is safe when running version 4.3.0 or later, which patches three high-severity denial of service issues found in 4.2.3 and earlier: a ReDoS in filename parsing, a prototype pollution crash, and an uncaught URIError from malformed percent-encoding in filename* parameters. Any service accepting multipart uploads on an older version remains exposed and should upgrade immediately. Developers choosing upload libraries can weigh security track records like this one on daily.dev."}}]} ```