CVE-2026-99999: ipv4: validate checksum_start before completing checksum
- Is it exploited?
Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of . If CISA adds it, this page shows it as known exploited.
- How likely is exploitation in the next 30 days?
- 0.8%
Up from 0.3% on .
EPSS score, percentile 56.1 of all scored records. A probability estimated by FIRST, not a report of exploitation.
- How severe?
- 9.3 Critical
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA has set no required action, because the vulnerability is not in KEV.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- 2.6.27
Unaffected before 2.6.27; 5.10.272; 5.15.223; 6.1.190; 6.6.159; 6.12.113; and 3 more
Source: CISA KEV 2026.10.28, as of ; FIRST EPSS, as of ; CVE List, as of . About the data.
What to do
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
This summary is based on the CVE record as of . Check the vendor's advisory before you act: affected versions and fixes can change.
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from f43798c27684 to before a464d950f31c |
| Affected | from f43798c27684 to before 0fab003ef469 |
| Affected | from f43798c27684 to before 94524b7b3269 |
| Affected | from f43798c27684 to before a65f69e0f38f |
| Affected | from f43798c27684 to before 32a8b0adaa18 |
| Affected | from f43798c27684 to before f3e835af6226 |
| Affected | from f43798c27684 to before c3e334647461 |
| Affected | from f43798c27684 to before 6785011f8b16 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 2.6.27 |
| Unaffected | before 2.6.27 |
| Unaffected | 5.10.272 |
| Unaffected | 5.15.223 |
| Unaffected | 6.1.190 |
| Unaffected | 6.6.159 |
| Unaffected | 6.12.113 |
| Unaffected | 6.18.57 |
| Unaffected | 7.2.11 |
| Unaffected | 7.3 |
Versions not listed are: affected.
Versions the record lists as unaffected: 5.10.272, 5.15.223, 6.1.190, 6.6.159, 6.12.113, 6.18.57, 7.2.11, 7.3.
Source: CVE List, as of . About the data.
About this vulnerability
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…
Summary: CVE record, as of .
- CISA has not added CVE-2026-99999 to its Known Exploited Vulnerabilities (KEV) catalog, as of 28 Oct 2026.
- The CVE record was published on 15 Oct 2026.
- The CVE record carries a CVSS v3.1 base score of 9.3 (Critical), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.8% (percentile 56.1), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
- CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact total.
Source: CISA KEV 2026.10.28, as of ; CVE List, as of ; FIRST EPSS, as of . About the data.
Description
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.
Source: CVE List, as of . About the data.
Weakness
CWE-20
- CWE-20: Improper Input Validation
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| CVE record last updated |
References
10
Known exploited Linux vulnerabilities
- CVE-2026-46300: Linux Kernel Missing Initialization of a Variable Vulnerability
- CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
- CVE-2025-39964: Linux Kernel Race Condition Vulnerability
- CVE-2026-53266: Linux Kernel Out-of-Bounds Write Vulnerability
- CVE-2026-53362: Linux Kernel Unspecified Vulnerability