CVE-2026-99999
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.
- CVSS
- 9.3Criticalscored by the publisher (CNA)
- Exploited in the wild
- Not knownUnvetted proof-of-concept code on GitHub; not in CISA KEV
- EPSS
- 0.79%chance of exploitation in the next 30 daystop 44% of scored CVEsFIRST score of 11 Nov 2026
- Fix
- Fixed in < 2.6.27, >= 5.10.272 and <= 5.10.*, >= 5.15.223 and <= 5.15.*per the vendor; 6 more listed below
- Published
- 15 Oct 2026analysed here 12 Nov 2026
Do first. Upgrade to a fixed release: < 2.6.27, >= 5.10.272 and <= 5.10.*, >= 5.15.223 and <= 5.15.*, >= 6.1.190 and <= 6.1.* (and 5 more below).
Summary
Triage
The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.
Affected products
| Product | Affected versions | Vendor says fixed in |
|---|---|---|
| Linux | >= f43798c27684ab925adde7d8acc34c78c6e50df8 and < a464d950f31c89565cbaae038cc60db04fe01956>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < 0fab003ef4698e0628060a45a48f14b43ba2a40a>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < 94524b7b32691de2e2ce162c04d6cbc9106e5cbf>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < a65f69e0f38ffbed1b128029e09097436416dc8b>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < 32a8b0adaa18e52aaa0b246b5ffe683075354dbb>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < f3e835af6226f1dd12160cbd696081e9b6155de0>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < c3e33464746166264334641dc850a36eef7e6326>= f43798c27684ab925adde7d8acc34c78c6e50df8 and < 6785011f8b16abf40b1e9d8b2e332232b3e688222.6.27Vendor says fixed in: < 2.6.27, >= 5.10.272 and <= 5.10.*, >= 5.15.223 and <= 5.15.*, >= 6.1.190 and <= 6.1.*, >= 6.6.159 and <= 6.6.*, >= 6.12.113 and <= 6.12.*, >= 6.18.57 and <= 6.18.*, >= 7.2.11 and <= 7.2.*, >= 7.3 and <= * |
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
Fix and mitigation
WAF and other mitigations
Can a WAF block it? No. The attack needs local access to the machine, so a WAF is not on its path.
Also consider: patch
Based on the attack vector (local or physical access). We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Remediation steps (AI-written)
Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.
Exploitation evidence
- CISA KEV catalog
- Not listed as of our last sync.
- Public exploit code
- Unvetted proof-of-concept code on GitHub: 14 GitHub proofs of concept
- CISA SSVC
- exploitation none, automatable no, technical impact totalAssessed by CISA 16 Oct 2026 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.
GitHub proofs of concept
- PeronGH/CVE-2026-9999921 stars
- 01luyicheng/CVE-2026-999995 stars
- Quaerendir/cve-2026-99999-audit3 stars
- MChorfa/csumguard2 stars
and 10 more repositories
Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.
Timeline
- 15 Oct 2026Published
- 16 Oct 2026First proof-of-concept repository on GitHub (unvetted)same day later
- 16 Oct 2026CISA SSVC assessment: exploitation none1 day later
- 24 Oct 2026CVE record last updated8 days later
- 12 Nov 2026Analysed by vulneraibility.com19 days later
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
| Metric | Value | What it means |
|---|---|---|
| Attack vector | LocalLocal access required (shell, logged-in user). | Local access required (shell, logged-in user). |
| Attack complexity | LowRepeatable attack, no special conditions. | Repeatable attack, no special conditions. |
| Privileges required | NoneThe attacker needs no prior access. | The attacker needs no prior access. |
| User interaction | NoneNo victim action needed. | No victim action needed. |
| Scope | ChangedImpact crosses a security boundary into other components. | Impact crosses a security boundary into other components. |
| Confidentiality | HighTotal data disclosure possible. | Total data disclosure possible. |
| Integrity | HighComplete modification possible. | Complete modification possible. |
| Availability | HighFull outage possible. | Full outage possible. |
Common questions
Is CVE-2026-99999 being exploited?
Not confirmed. CVE-2026-99999 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.79% probability of exploitation in the next 30 days.
How severe is CVE-2026-99999?
CVE-2026-99999 is rated Critical with a CVSS score of 9.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-99999?
Not known from our data. No patch reference has been recorded for CVE-2026-99999, which is not the same as no patch existing — a fix may have shipped without a tagged reference, or after this record was written. The vendor advisory is the only authority on whether a fix exists, and mitigations may be available regardless.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
References
11 references in the CVE record, grouped by the tags the record gives them.
Other links (11)
- git.kernel.org /stable/c/a464d950f31c89565cbaae038cc60db04fe01956
- git.kernel.org /stable/c/0fab003ef4698e0628060a45a48f14b43ba2a40a
- git.kernel.org /stable/c/94524b7b32691de2e2ce162c04d6cbc9106e5cbf
- git.kernel.org /stable/c/a65f69e0f38ffbed1b128029e09097436416dc8b
- git.kernel.org /stable/c/32a8b0adaa18e52aaa0b246b5ffe683075354dbb
- git.kernel.org /stable/c/f3e835af6226f1dd12160cbd696081e9b6155de0
Show 5 more
- git.kernel.org /stable/c/c3e33464746166264334641dc850a36eef7e6326
- git.kernel.org /stable/c/6785011f8b16abf40b1e9d8b2e332232b3e68822
- pwn.ai /blog/pwnescape
- vercel.com /blog/findings-from-the-1-million-dollar-vercel-sandbox-challenge
- openwall.com /lists/oss-security/2026/10/15/5
Where the data on this page comes from
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- PoC-in-GitHub: GitHub repositories that claim a proof of concept
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
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