--- title: This bug is genuinely neat | daily.dev description: A newly disclosed vulnerability in U-Boot, the widely used embedded bootloader, is a stack buffer underflow triggered during FIT image signature verification,... canonical: https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: This bug is genuinely neat | daily.dev og:description: A newly disclosed vulnerability in U-Boot, the widely used embedded bootloader, is a stack buffer underflow triggered during FIT image signature verification,... og:url: https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy og:image: https://api.daily.dev/og/posts/4Uw8FW0VY.png og:image:alt: This bug is genuinely neat 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. # This bug is genuinely neat **[Low Level Learning](https://daily.dev/sources/lowlevellearning)** · 12 min read · 1 upvotes · 0 comments ## Summary A newly disclosed vulnerability in U-Boot, the widely used embedded bootloader, is a stack buffer underflow triggered during FIT image signature verification, specifically in the FDT find regions logic. The bug abuses an error path in FDT getname where a negative error code gets written into a length field, causing a pointer to move backward across stack frames until it overwrites a saved return address, enabling arbitrary code execution. Because this occurs inside the code responsible for verifying cryptographic signatures on boot images, a successful exploit can bypass secure boot signature checks entirely, letting unsigned or attacker-controlled firmware run on affected devices. The vulnerability was discovered and published by Binarly, and no patch exists yet at the time of the walkthrough, which also includes a live demo compiling the vulnerable U-Boot in QEMU and gaining control of the program counter. The video also discusses whether Rust could have prevented the bug, concluding that Rust's Result type would address the underlying C pattern of overloading an output slot with an error code, though embedded bootloader code still requires unsafe code for raw MMIO access. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is the U-Boot stack buffer underflow vulnerability in FIT image signature verification? It is a bug in U-Boot's fdt_find_regions function where a failed fdt_getname call writes an error code (FDT_ERR_BADSTRUCTURE, a large negative value) into a length output pointer instead of the actual name length. Because later code adds this length to a cursor pointer, the pointer moves backward through the stack rather than forward, letting an attacker craft malformed FIT image section names to eventually overwrite a saved return address and hijack the program counter during signature verification, bypassing the trust chain. No patch was available at the time of disclosure. _Bootloader engineers tracking U-Boot security fixes can follow patch status and writeups like this through daily.dev._ ### Would writing U-Boot in Rust have prevented this stack buffer underflow bug? Partially. Rust's Result type would likely prevent the specific root cause, which is the classic C pattern of reusing an error-code value in the same slot meant for a valid length, since Rust forces you to distinguish an error from a success value rather than overloading one field. However, bootloader code still requires unsafe blocks for raw MMIO and hardware access even when using peripheral access or hardware abstraction crates, so Rust would reduce but not eliminate this class of risk. _Developers weighing Rust for embedded and bootloader code can compare these safety trade-offs on daily.dev._ ## Similar posts on daily.dev - [New U-Boot flaws could enable stealthy firmware attacks](https://daily.dev/posts/new-u-boot-flaws-could-enable-stealthy-firmware-attacks-306qqf8os) · BleepingComputer · 1 upvotes · 0 comments - [Of Boot Vectors and Double Glitches: Bypassing RP2350's Secure Boot](https://daily.dev/posts/of-boot-vectors-and-double-glitches-bypassing-rp2350-s-secure-boot-j9qyv0m0w) · Hacker News · 1 upvotes · 0 comments --- Tags: [#security](https://daily.dev/tags/security), [#embedded](https://daily.dev/tags/embedded) [View this post on daily.dev](https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy) ```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":"This bug is genuinely neat","url":"https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy"},"datePublished":"2026-08-12T14:40:16.140Z","dateModified":"2026-09-14T09:19:58.801Z","description":"A newly disclosed vulnerability in U-Boot, the widely used embedded bootloader, is a stack buffer underflow triggered during FIT image signature verification,...","image":"https://i.ytimg.com/vi/XuOVcKPVZx4/sddefault.jpg","thumbnailUrl":"https://i.ytimg.com/vi/XuOVcKPVZx4/sddefault.jpg","isAccessibleForFree":true,"articleSection":"Low Level Learning","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":"Low Level Learning","logo":"https://media.daily.dev/image/upload/s--pjLyMMmx--/f_auto/v1724394406/logos/lowlevellearning","url":"https://daily.dev/sources/lowlevellearning"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"security,embedded","timeRequired":"PT12M","video":{"@type":"VideoObject","name":"This bug is genuinely neat","description":"A newly disclosed vulnerability in U-Boot, the widely used embedded bootloader, is a stack buffer underflow triggered during FIT image signature verification,...","thumbnailUrl":"https://i.ytimg.com/vi/XuOVcKPVZx4/sddefault.jpg","uploadDate":"2026-08-12T14:40:16.140Z","duration":"PT12M","url":"https://api.daily.dev/r/4Uw8FW0VY","embedUrl":"https://www.youtube.com/embed/XuOVcKPVZx4"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Low Level Learning","item":"https://daily.dev/sources/lowlevellearning"},{"@type":"ListItem","position":3,"name":"This bug is genuinely neat"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/this-bug-is-genuinely-neat-4uw8fw0vy#faq","mainEntity":[{"@type":"Question","name":"What is the U-Boot stack buffer underflow vulnerability in FIT image signature verification?","acceptedAnswer":{"@type":"Answer","text":"It is a bug in U-Boot's fdt_find_regions function where a failed fdt_getname call writes an error code (FDT_ERR_BADSTRUCTURE, a large negative value) into a length output pointer instead of the actual name length. Because later code adds this length to a cursor pointer, the pointer moves backward through the stack rather than forward, letting an attacker craft malformed FIT image section names to eventually overwrite a saved return address and hijack the program counter during signature verification, bypassing the trust chain. No patch was available at the time of disclosure. Bootloader engineers tracking U-Boot security fixes can follow patch status and writeups like this through daily.dev."}},{"@type":"Question","name":"Would writing U-Boot in Rust have prevented this stack buffer underflow bug?","acceptedAnswer":{"@type":"Answer","text":"Partially. Rust's Result type would likely prevent the specific root cause, which is the classic C pattern of reusing an error-code value in the same slot meant for a valid length, since Rust forces you to distinguish an error from a success value rather than overloading one field. 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