Critical

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

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.

Published Oct 15, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

Technical severity (critical)+10

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

—

No EPSS score.

Affects

Linux

CVSS base

9.3

Critical · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < a464d950f31c89565cbaae038cc60db04fe01956≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < 0fab003ef4698e0628060a45a48f14b43ba2a40a≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < 94524b7b32691de2e2ce162c04d6cbc9106e5cbf≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < a65f69e0f38ffbed1b128029e09097436416dc8b≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < 32a8b0adaa18e52aaa0b246b5ffe683075354dbb≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < f3e835af6226f1dd12160cbd696081e9b6155de0≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < c3e33464746166264334641dc850a36eef7e6326≥ f43798c27684ab925adde7d8acc34c78c6e50df8 and < 6785011f8b16abf40b1e9d8b2e332232b3e68822 and 1 more version 2.6.27	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Local

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
9.3	CVSS 3.1	Critical	2.5	6.0	416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
9.3	CVSS 3.1	Critical	—	—	Linux via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.

endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

2026
Affected products added · linux/linux
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 9.3
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Received
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · Alertas do Telegram
CVE published
Oct 15, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

1× References added · Oct 15, 2026 – Oct 15, 2026
1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

10 on the record

git.kernel.org/stable/c/a464d950f31c89565cbaae038cc60db04fe01956
NIST National Vulnerability Database
git.kernel.org/stable/c/a65f69e0f38ffbed1b128029e09097436416dc8b
NIST National Vulnerability Database
git.kernel.org/stable/c/6785011f8b16abf40b1e9d8b2e332232b3e68822
NIST National Vulnerability Database
pwn.ai/blog/Pwnescape
NIST National Vulnerability Database
vercel.com/blog/findings-from-the-1-million-dollar-vercel-sandbox-challenge
NIST National Vulnerability Database
git.kernel.org/stable/c/c3e33464746166264334641dc850a36eef7e6326
NIST National Vulnerability Database
git.kernel.org/stable/c/94524b7b32691de2e2ce162c04d6cbc9106e5cbf
NIST National Vulnerability Database
git.kernel.org/stable/c/f3e835af6226f1dd12160cbd696081e9b6155de0
NIST National Vulnerability Database
git.kernel.org/stable/c/32a8b0adaa18e52aaa0b246b5ffe683075354dbb
NIST National Vulnerability Database
git.kernel.org/stable/c/0fab003ef4698e0628060a45a48f14b43ba2a40a
NIST National Vulnerability Database

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 3h
Unknown CVE-2026-98430 RDMA/efa: Keep admin queues alive while IRQ is registered 1d
Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No FIRST EPSS score.
No fixed version, patch or mitigation documented.
No CISA SSVC assessment.
No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-99999 is "ipv4: validate checksum_start before completing checksum", rated Critical. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.3 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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