# CVE-2026-99999: ipv4: validate checksum_start before completing checksum

> CVE-2026-99999: ipv4: validate checksum_start before completing checksum. CVSS 9.3 (CVSS 3.1), named in 3 status incident(s).

Canonical: https://rewindex.com/cve/CVE-2026-99999
Last updated: 2026-10-24T14:17:15Z

- Published: 2026-10-15 12:19 UTC · Updated: 2026-10-24 14:17 UTC · Assigner: Linux
- CVSS: 9.3 (CVSS 3.1) · Severity: Critical · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- EPSS: 0.79%, 56th percentile (scored 2026-10-25)
- CISA KEV: no

## Description

In the Linux kernel, the following vulnerability has been resolved: ipv4: validate checksum\_start before completing checksum If a packet with bad checksum metadata gets into the ipv4 stack, skb\_checksum\_help can corrupt the network header and cause a bunch of mischief. This was discovered and reported by Paulos, and has been reporoduced by others independently since. We really shouldn't allow such packets in, but as a defence in depth measure, let's also check before we complete the checksum. A more complete validation at input is forthcoming, but needs more work.

## Affected vendors and products

- Linux: Linux

## Tracked companies

- [Amazon Web Services](https://rewindex.com/company/aws.md)

## Status incidents that name it

- 2026-10-16 16:22 UTC [Fly.io: Platform Wide Rolling Host Reboots](https://rewindex.com/company/fly-io/incidents/01M52RAWMVC0NKEBRDKC3VXT3K.md) (names this CVE): “…elevated primary standby switchovers during this period. We As a mitigation measure for PwnEscape (Linux Kernel CVE-2026-99999), host restarts are continuing in phases across all regions. At this point, more than 90% of the fleet has been…”
- 2026-10-16 06:00 UTC [Hetzner: CVE-2026-99999 (PwnEscape)](https://rewindex.com/company/hetzner/incidents/dc591a73-758c-4b18-a4a2-7ed98e7c6428.md) (names this CVE): “CVE-2026-99999 (PwnEscape) Start: 2026-10-16T06:00:00+00:00 On Thursday, October 15, 2026, a security vulnerability in the Linux…”
- 2026-10-15 17:27 UTC [Linode (Akamai): (PwnEscape) Guest-to-Host KVM Escape \[CVE-2026-99999\]](https://rewindex.com/company/linode-akamai/incidents/zp71823t318w.md) (names this CVE): “(PwnEscape) Guest-to-Host KVM Escape \[CVE-2026-99999\] Akamai has completed patching Compute hypervisors for the known vulnerabilities related to CVE-2026-99999, also…”

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-99999)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-99999)
- [https://git.kernel.org/stable/c/0fab003ef4698e0628060a45a48f14b43ba2a40a](https://git.kernel.org/stable/c/0fab003ef4698e0628060a45a48f14b43ba2a40a)
- [https://git.kernel.org/stable/c/32a8b0adaa18e52aaa0b246b5ffe683075354dbb](https://git.kernel.org/stable/c/32a8b0adaa18e52aaa0b246b5ffe683075354dbb)
- [https://git.kernel.org/stable/c/6785011f8b16abf40b1e9d8b2e332232b3e68822](https://git.kernel.org/stable/c/6785011f8b16abf40b1e9d8b2e332232b3e68822)
- [https://git.kernel.org/stable/c/94524b7b32691de2e2ce162c04d6cbc9106e5cbf](https://git.kernel.org/stable/c/94524b7b32691de2e2ce162c04d6cbc9106e5cbf)
- [https://git.kernel.org/stable/c/a464d950f31c89565cbaae038cc60db04fe01956](https://git.kernel.org/stable/c/a464d950f31c89565cbaae038cc60db04fe01956)
- [https://git.kernel.org/stable/c/a65f69e0f38ffbed1b128029e09097436416dc8b](https://git.kernel.org/stable/c/a65f69e0f38ffbed1b128029e09097436416dc8b)
- [https://git.kernel.org/stable/c/c3e33464746166264334641dc850a36eef7e6326](https://git.kernel.org/stable/c/c3e33464746166264334641dc850a36eef7e6326)
- [https://git.kernel.org/stable/c/f3e835af6226f1dd12160cbd696081e9b6155de0](https://git.kernel.org/stable/c/f3e835af6226f1dd12160cbd696081e9b6155de0)
- [https://pwn.ai/blog/pwnescape](https://pwn.ai/blog/pwnescape)
- [https://vercel.com/blog/findings-from-the-1-million-dollar-vercel-sandbox-challenge](https://vercel.com/blog/findings-from-the-1-million-dollar-vercel-sandbox-challenge)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-99999 · Markdown: https://rewindex.com/cve/CVE-2026-99999.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-99999 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:13:37.454Z