--- title: How a single typo led to RCE in Firefox – kqx | daily.dev description: A single-character typo in Firefox's SpiderMonkey WebAssembly GC implementation led to a critical remote code execution vulnerability. The bug involved using... canonical: https://daily.dev/posts/uupmrngpi twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How a single typo led to RCE in Firefox – kqx | daily.dev og:description: A single-character typo in Firefox's SpiderMonkey WebAssembly GC implementation led to a critical remote code execution vulnerability. The bug involved using... og:url: https://daily.dev/posts/uupmrngpi og:image: https://api.daily.dev/og/posts/UUPMRnGPi.png og:image:alt: Post cover image 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. # How a single typo led to RCE in Firefox – kqx **[Master Yoda](https://daily.dev/sources/biixj2rltcrx7bbvxfw0d)** · [@pump1it](https://daily.dev/pump1it) · 2 upvotes · 0 comments ## Summary A single-character typo in Firefox's SpiderMonkey WebAssembly GC implementation led to a critical remote code execution vulnerability. The bug involved using bitwise AND (&) instead of OR (|) when setting a forwarding pointer, causing out-of-line arrays to be misidentified as inline arrays. This created a use-after-free condition exploitable through heap spraying to achieve arbitrary read/write primitives and ultimately RCE in the Firefox renderer process. The vulnerability only affected Firefox 149 Nightly and was patched before reaching release versions. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Undetected Firefox WebAssembly Flaw Put 180 Million Users at Risk](https://daily.dev/posts/undetected-firefox-webassembly-flaw-put-180-million-users-at-risk-dxowk1wpf) · Security Boulevard · 14 upvotes · 0 comments - [NGINX Rift: Achieving NGINX Remote Code Execution via an 18-Year-Old Vulnerability](https://daily.dev/posts/nginx-rift-achieving-nginx-remote-code-execution-via-an-18-year-old-vulnerability-stsyzlmrh) · Lobsters · 16 upvotes · 0 comments - [RCE As a Feature](https://daily.dev/posts/rce-as-a-feature-xeeuukhv1) · The Daily WTF · 0 upvotes · 0 comments --- Tags: [#security](https://daily.dev/tags/security), [#javascript](https://daily.dev/tags/javascript), [#webassembly](https://daily.dev/tags/webassembly), [#firefox](https://daily.dev/tags/firefox) [View this post on daily.dev](https://daily.dev/posts/uupmrngpi) ```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":"DiscussionForumPosting","mainEntityOfPage":"https://daily.dev/posts/uupmrngpi","headline":"How a single typo led to RCE in Firefox – kqx","text":"Shared: How a single typo led to RCE in Firefox – kqx","url":"https://daily.dev/posts/uupmrngpi","datePublished":"2026-02-18T11:51:13.234Z","dateModified":"2026-02-18T11:51:13.238Z","author":{"@type":"Person","name":"Master Yoda","url":"https://daily.dev/pump1it","image":"https://media.daily.dev/image/upload/s--QoEA3qeD--/f_auto/v1739976473/avatars/avatar_BiIXJ2RLtCrx7bbvXFw0D","interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"EndorseAction"},"userInteractionCount":2700}},"image":"https://media.daily.dev/image/upload/s--VDukGCjf--/f_auto/v1722860399/public/Placeholder%2002","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":2},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"sharedContent":{"@type":"WebPage","url":"https://api.daily.dev/r/tKFkhLwCA"},"isPartOf":{"@type":"WebPage","url":"https://daily.dev/sources/biixj2rltcrx7bbvxfw0d","name":"Master Yoda"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Master Yoda","item":"https://daily.dev/sources/biixj2rltcrx7bbvxfw0d"},{"@type":"ListItem","position":3,"name":"How a single typo led to RCE in Firefox – kqx"}]} ```