CVE-2026-99999: In the Linux kernel, the following vulnerability has been resolved: ipv4: validate checksum_start before comp

This week

CRITICAL 9.3WATCHLIST

CVE-2026-99999 is a critical-severity flaw (CVSS 9.3) affecting affected software. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Critical severity
Public exploit reference
Covered by 3 security sources
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.3 (Critical)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.8% (top 44%)
CISA exploited list	No
Weakness	CWE-20
Published	2026-10-15
Last modified	2026-10-19

Publisher (CNA): kernel.org

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Timeline

2026-10-15 13:17 UTCPublished CVE record published
2026-10-19 22:17 UTCUpdated Record last modified

Exact fixes by distribution

Fedora ELN · edk2 · FIXED · 20260812-12.eln159 · FEDORA-2026-e316b6370a · source

sudo dnf upgrade --advisory=FEDORA-2026-e316b6370a

Fedora 46 · perl-Mojo-DOM58 · FIXED · 3.003-1.fc46 · FEDORA-2026-d5412af3de · source

sudo dnf upgrade --advisory=FEDORA-2026-d5412af3de

Debian 12 · linux · FIXED · 6.1.190-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.1.190-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · linux · FIXED · 6.12.113-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.12.113-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · linux-6.12 · FIXED · 6.12.113-1~deb12u1

sudo apt update && sudo apt install --only-upgrade linux-6.12 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux-6.12)" ge "6.12.113-1~deb12u1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · kernel · FIXED · kernel-6.12.0-211.67.1.el10_2

sudo dnf upgrade --advisory=RHSA-2026:85321 rpm -q kernel

RHEL 10.0 Extended Update Support · kernel · FIXED · kernel-6.12.0-55.112.1.el10_0

sudo dnf upgrade --advisory=RHSA-2026:85979 rpm -q kernel

RHEL 7 Extended Lifecycle Support · kernel-rt · FIXED · kernel-rt-3.10.0-1160.167.2.rt56.1320.el7

sudo dnf upgrade --advisory=RHSA-2026:88204 rpm -q kernel-rt

RHEL 7 Extended Lifecycle Support · kernel · FIXED · kernel-3.10.0-1160.167.2.el7

sudo dnf upgrade --advisory=RHSA-2026:88206 rpm -q kernel

RHEL 8 · kernel · FIXED · kernel-4.18.0-553.178.1.el8_10

sudo dnf upgrade --advisory=RHSA-2026:89083 rpm -q kernel

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2026-3197 · source

sudo dnf update --advisory=ALAS2023-2026-3197

Amazon Linux 2 · see advisory · FIXED · ALAS2-2026-3962 · source

sudo yum update --advisory=ALAS2-2026-3962

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: PeronGH/CVE-2026-99999 (18 stars)
GitHub PoC: 01luyicheng/CVE-2026-99999 (5 stars)
GitHub PoC: MChorfa/csumguard (2 stars)

Advisories and coverage

Official advisories

AWS Security Bulletins: Issue in the Linux kernel virtio-net/TAP networking path affecting KVM-based hypervisors 2026-10-15
Amazon Linux 2 ALAS: ALAS2KERNEL-5.4-2026-131 (important): kernel 2026-10-01
Amazon Linux 2 ALAS: ALAS2-2026-3962 (important): kernel 2026-10-01

Research and news

The Register Security: Linux KVM guest-host escape rated critical, may represent a new way to attack penguin-powered networking 2026-10-19

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-99999?

No fixed release is listed yet. Watch the vendor advisory and apply any mitigation shown on this page.

Is CVE-2026-99999 being exploited?

CVE-2026-99999 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-99999 affect?

CVE-2026-99999 affects affected software. Severity is critical (CVSS 9.3). 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

How urgent is CVE-2026-99999?

Priority 60/100. Critical severity; Public exploit reference; Covered by 3 security sources; On your watchlist

Software pages

Linux kernel vulnerabilities

References

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