--- title: Vercel's $1M bounty bought a Linux VM-escape zero-day description: A critical Linux kernel vulnerability, nicknamed PwnEscape (CVE-2026-99999), was found in skb_checksum_help() during Vercel's $1M bug bounty challenge against... canonical: https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Vercel's $1M bounty bought a Linux VM-escape zero-day | daily.dev og:description: A critical Linux kernel vulnerability, nicknamed PwnEscape (CVE-2026-99999), was found in skb_checksum_help() during Vercel's $1M bug bounty challenge against... og:url: https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6 og:image: https://api.daily.dev/og/posts/F9b6nSIP6.png og:image:alt: Vercel's $1M bounty bought a Linux VM-escape zero-day 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. # Vercel's $1M bounty bought a Linux VM-escape zero-day **[Trends](https://daily.dev/sources/trends)** · 2 min read · 0 upvotes · 0 comments ## Summary A critical Linux kernel vulnerability, nicknamed PwnEscape (CVE-2026-99999), was found in skb_checksum_help() during Vercel's $1M bug bounty challenge against its Sandbox product. The flaw, a time-of-check/time-of-use bug in checksum offload, lets an attacker corrupt IPv4 header metadata to leak host memory and chain into host-root code execution from inside a compromised VM. Researcher Paulos Yibelo warns the bug is not hypervisor-specific and expects exploits targeting weaker configurations within weeks. Greg Kroah-Hartman shipped patches across seven stable kernel branches (5.10 through 7.2) plus mainline. The bounty program drew 1,285 reports in two weeks and paid out $242,000, also surfacing a cross-tenant disk snapshot restore flaw and a device-mapper bug found by a Vercel intern. A separate Trail of Bits audit found the virtualization boundary itself sound but recommended structural defense-in-depth improvements, since the kernel bug bypassed the sandbox's architecture entirely. ## Content The loudest warning comes from the researcher himself. Paulos Yibelo, who found the bug, says the flaw is not hypervisor-specific and expects exploits aimed at weaker configurations within weeks. If you run VMs, treat the patch as urgent. ## What got fixed Greg Kroah-Hartman shipped seven stable kernels on Thursday: 7.2.11, 6.18.57, 6.12.113, 6.6.159, 6.1.190, 5.15.223 and 5.10.272. The headline fix is CVE-2026-99999, nicknamed PwnEscape, in `skb_checksum_help()`. Patch author Michael S. Tsirkin says an IPv4 packet with bad checksum metadata could corrupt the network header, with "disruptive effects." Everyone is advised to upgrade. The mechanism is a time-of-check/time-of-use problem in checksum offload. Attacker-controlled metadata can corrupt an IPv4 header after it has already been validated. That leaks adjacent host memory, and it can be chained into host-root code execution from inside a compromised VM. The upstream fix (commit 6785011f8b16) adds validation before checksum-completion operations. It is backported to all seven stable branches, from 5.10 to 7.2, plus mainline. ## How it surfaced Vercel ran a public $1M bounty challenge against its Sandbox product. It drew 1,285 reports in two weeks and paid out $242,000. Yibelo's find stood out: leaking host memory, crashing the host and executing code on the host from inside a microVM, demonstrated against production sandboxes. Vercel says no customer data was accessed. The zero-day wasn't the only result: - A cross-tenant disk snapshot restore flaw that abused a trust-boundary violation. - A device-mapper storage bug found internally by a Vercel intern. ## The audit angle Trail of Bits spent four engineer-weeks on a white-box review. Its verdict: the virtualization boundary itself is sound. But it still recommended structural fixes around guest trust, policy enforcement and defense-in-depth, specifically so the next kernel zero-day doesn't hand over the host. That is the uncomfortable takeaway. A well-built sandbox passed review, and a bug in the upstream networking stack still walked right through it. Isolation is only as good as the kernel underneath it, and a bounty program found what the audit's scope was never going to. ## Questions this post answers ### What is CVE-2026-99999 PwnEscape and which Linux kernel versions are affected? PwnEscape is a Linux kernel vulnerability in skb_checksum_help() involving a time-of-check/time-of-use flaw in checksum offload, where attacker-controlled metadata can corrupt an already-validated IPv4 header, leaking host memory and enabling host-root code execution from inside a VM. It was patched in stable kernels 7.2.11, 6.18.57, 6.12.113, 6.6.159, 6.1.190, 5.15.223, and 5.10.272 via commit 6785011f8b16. _daily.dev helps engineers patching VM-escape bugs track kernel CVEs across every stable branch._ ### How did Vercel's bug bounty program find the PwnEscape kernel vulnerability? Vercel ran a public $1M bounty challenge against its Sandbox product, drawing 1,285 reports in two weeks and paying out $242,000 total. Researcher Paulos Yibelo's submission demonstrated leaking host memory, crashing the host, and executing code on the host from inside a microVM against production sandboxes, with Vercel confirming no customer data was accessed. _Teams weighing bug bounty payouts against audit costs follow results like this on daily.dev._ ### Is a formal security audit enough to catch kernel-level VM escape vulnerabilities? No, a four-engineer-week white-box review by Trail of Bits concluded the virtualization boundary itself was sound, yet a bug in the upstream Linux networking stack still bypassed it entirely. The audit recommended structural fixes around guest trust, policy enforcement, and defense-in-depth so a future kernel zero-day would not immediately compromise the host. _daily.dev keeps sandbox and isolation engineers current on gaps between audits and real-world exploits._ ## Similar posts on daily.dev - [Google pays $250K for Linux vulnerability allowing guest VM escapes](https://daily.dev/posts/google-pays-250k-for-linux-vulnerability-allowing-guest-vm-escapes-dp9gdnmga) · Ars Technica · 2 upvotes · 0 comments --- Tags: [#linux](https://daily.dev/tags/linux), [#vercel](https://daily.dev/tags/vercel) [View this post on daily.dev](https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6) ```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":"Vercel's $1M bounty bought a Linux VM-escape zero-day","url":"https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6"},"datePublished":"2026-10-16T12:03:01.151Z","dateModified":"2026-10-16T12:03:40.153Z","description":"A critical Linux kernel vulnerability, nicknamed PwnEscape (CVE-2026-99999), was found in skb_checksum_help() during Vercel's $1M bug bounty challenge against...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/3965333846c96dcb3112a1245f7adf2b?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/3965333846c96dcb3112a1245f7adf2b?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Trends","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":"Trends","logo":"https://media.daily.dev/image/upload/s--ZfSp3asX--/f_auto,q_auto/v1780996004/logos/trends?_a=BAMAMiWQ0","url":"https://daily.dev/sources/trends"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"linux,vercel","timeRequired":"PT2M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Trends","item":"https://daily.dev/sources/trends"},{"@type":"ListItem","position":3,"name":"Vercel's $1M bounty bought a Linux VM-escape zero-day"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/vercel-s-1m-bounty-bought-a-linux-vm-escape-zero-day-f9b6nsip6#faq","mainEntity":[{"@type":"Question","name":"What is CVE-2026-99999 PwnEscape and which Linux kernel versions are affected?","acceptedAnswer":{"@type":"Answer","text":"PwnEscape is a Linux kernel vulnerability in skb_checksum_help() involving a time-of-check/time-of-use flaw in checksum offload, where attacker-controlled metadata can corrupt an already-validated IPv4 header, leaking host memory and enabling host-root code execution from inside a VM. It was patched in stable kernels 7.2.11, 6.18.57, 6.12.113, 6.6.159, 6.1.190, 5.15.223, and 5.10.272 via commit 6785011f8b16. daily.dev helps engineers patching VM-escape bugs track kernel CVEs across every stable branch."}},{"@type":"Question","name":"How did Vercel's bug bounty program find the PwnEscape kernel vulnerability?","acceptedAnswer":{"@type":"Answer","text":"Vercel ran a public $1M bounty challenge against its Sandbox product, drawing 1,285 reports in two weeks and paying out $242,000 total. Researcher Paulos Yibelo's submission demonstrated leaking host memory, crashing the host, and executing code on the host from inside a microVM against production sandboxes, with Vercel confirming no customer data was accessed. Teams weighing bug bounty payouts against audit costs follow results like this on daily.dev."}},{"@type":"Question","name":"Is a formal security audit enough to catch kernel-level VM escape vulnerabilities?","acceptedAnswer":{"@type":"Answer","text":"No, a four-engineer-week white-box review by Trail of Bits concluded the virtualization boundary itself was sound, yet a bug in the upstream Linux networking stack still bypassed it entirely. The audit recommended structural fixes around guest trust, policy enforcement, and defense-in-depth so a future kernel zero-day would not immediately compromise the host. daily.dev keeps sandbox and isolation engineers current on gaps between audits and real-world exploits."}}]} ```