--- title: CVE-2026-1678: DNS Parser Overflow in Zephyr | daily.dev description: A detailed writeup of CVE-2026-1678, a critical out-of-bounds write (CVSS 9.4) in Zephyr RTOS's DNS name parser function dns_unpack_name(). The bug stems from... canonical: https://daily.dev/posts/cve-2026-1678-dns-parser-overflow-in-zephyr-rqcl8djgk twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: CVE-2026-1678: DNS Parser Overflow in Zephyr | daily.dev og:description: A detailed writeup of CVE-2026-1678, a critical out-of-bounds write (CVSS 9.4) in Zephyr RTOS's DNS name parser function dns_unpack_name(). The bug stems from... og:url: https://daily.dev/posts/cve-2026-1678-dns-parser-overflow-in-zephyr-rqcl8djgk og:image: https://api.daily.dev/og/posts/RqCl8dJgK.png og:image:alt: CVE-2026-1678: DNS Parser Overflow in Zephyr 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. # CVE-2026-1678: DNS Parser Overflow in Zephyr **[0xkato](https://daily.dev/sources/0xkato)** · 6 min read · 0 upvotes · 0 comments ## Summary A detailed writeup of CVE-2026-1678, a critical out-of-bounds write (CVSS 9.4) in Zephyr RTOS's DNS name parser function dns_unpack_name(). The bug stems from a stale bounds check: dest_size is captured once at the top of the function but never refreshed as the buffer fills with labels and dots. An attacker can craft a DNS message with five 63-byte labels that fits within the 512-byte UDP limit but overflows the 255-byte destination buffer by up to 200 bytes. With CONFIG_ASSERT disabled (the production default), the overflow is completely silent — no crash, just attacker-controlled memory corruption over the network with no authentication required. The fix, merged in PR #99683, moves the tailroom calculation inside the loop so it refreshes on every iteration. The post also offers advice to security researchers: look for stale size values, focus on format translation boundaries, and never treat standards compliance as a security guarantee. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [You gave me a u32. I gave you root. \(io](https://daily.dev/posts/you-gave-me-a-u32-i-gave-you-root-io-evofdoyif) · Hacker News · 2 upvotes · 0 comments - [CVE-2026-80213 \(resolv\): CVE-2026-80213](https://daily.dev/posts/cve-2026-80213-resolv-cve-2026-80213-t0mzi5omn) · RUBYLAND · 0 upvotes · 0 comments - [CVE-2025-68670: an RCE vulnerability in the xrdp server](https://daily.dev/posts/cve-2025-68670-an-rce-vulnerability-in-the-xrdp-server-6mkvp6bqq) · Securelist · 0 upvotes · 0 comments - [Cache poisoning vulnerabilities found in 2 DNS resolving apps](https://daily.dev/posts/cache-poisoning-vulnerabilities-found-in-2-dns-resolving-apps-6vkvn3cm5) · Ars Technica · 0 upvotes · 0 comments --- Tags: [#security](https://daily.dev/tags/security), [#dns](https://daily.dev/tags/dns) [View this post on daily.dev](https://daily.dev/posts/cve-2026-1678-dns-parser-overflow-in-zephyr-rqcl8djgk) ```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":"CVE-2026-1678: DNS Parser Overflow in Zephyr","url":"https://daily.dev/posts/cve-2026-1678-dns-parser-overflow-in-zephyr-rqcl8djgk","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/cve-2026-1678-dns-parser-overflow-in-zephyr-rqcl8djgk"},"datePublished":"2026-08-02T07:06:55.929Z","dateModified":"2026-08-02T07:19:34.994Z","description":"A detailed writeup of CVE-2026-1678, a critical out-of-bounds write (CVSS 9.4) in Zephyr RTOS's DNS name parser function dns_unpack_name(). The bug stems from...","image":"https://media.daily.dev/image/upload/s--0_ODbtD2--/f_auto/v1722860399/public/Placeholder%2008","thumbnailUrl":"https://media.daily.dev/image/upload/s--0_ODbtD2--/f_auto/v1722860399/public/Placeholder%2008","isAccessibleForFree":true,"articleSection":"0xkato","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":"0xkato","logo":"https://media.daily.dev/image/upload/s--4y20wV9B--/f_auto,q_auto/v1785654409/logos/0xkato","url":"https://daily.dev/sources/0xkato"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/cve-2026-1678-dns-parser-overflow-in-zephyr-rqcl8djgk","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"security,dns","timeRequired":"PT6M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"0xkato","item":"https://daily.dev/sources/0xkato"},{"@type":"ListItem","position":3,"name":"CVE-2026-1678: DNS Parser Overflow in Zephyr"}]} ```