CVE-2026-98621Network attack vectorHinoki check available

Memory corruption via reversed GUE checksum offsets

Published Oct 18, 2026 · Updated Oct 18, 2026

An offset-validation flaw in Linux kernel GUE processing allows remote attackers to corrupt memory via crafted checksum options. validate_gue_flags() accepts reversed REMCSUM offsets, causing subtraction in skb_remcsum_process() to underflow a 16-bit checksum offset. The documented two-byte out-of-bounds write requires GUE traffic forwarded with CHECKSUM_PARTIAL to a NETIF_F_HW_CSUM driver; code execution is not established.

CVSS severityUnavailable
Unscored
EPSS probability0.21%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

An offset-validation flaw in Linux kernel GUE processing allows remote attackers to corrupt memory via crafted checksum options. validate_gue_flags() accepts reversed REMCSUM offsets, causing subtraction in skb_remcsum_process() to underflow a 16-bit checksum offset. The documented two-byte out-of-bounds write requires GUE traffic forwarded with CHECKSUM_PARTIAL to a NETIF_F_HW_CSUM driver; code execution is not established.

The record

CVE
CVE-2026-98621
Published
Oct 18, 2026
Updated
Oct 18, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.0
  2. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <1d664be4ca49d1696e85239236f4988dfc4653c3
  3. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <1eeec0c51fd5598da44080ed96bbd9880021c28b
  4. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <2566866fc30965d915d0b52b5c3323b362619f0e
  5. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f
  6. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <43efb1f997e976f386aa89716f55870cd2cff9ad
  7. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <4b9bc21b2396c396d88dd909caaf73d5be6ff593
  8. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <97f907203321eee2cc9132d5c9eb47698fb41d35
  9. Affected versionversion=fe881ef11cf0220f118816181930494d484c4883 <c20f755338ca234e523dfc943719f194dfc1f903

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.0; version=fe881ef11cf0220f118816181930494d484c4883 <1d664be4ca49d1696e85239236f4988dfc4653c3; version=fe881ef11cf0220f118816181930494d484c4883 <1eeec0c51fd5598da44080ed96bbd9880021c28b; version=fe881ef11cf0220f118816181930494d484c4883 <2566866fc30965d915d0b52b5c3323b362619f0e; version=fe881ef11cf0220f118816181930494d484c4883 <40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f; version=fe881ef11cf0220f118816181930494d484c4883 <43efb1f997e976f386aa89716f55870cd2cff9ad; version=fe881ef11cf0220f118816181930494d484c4883 <4b9bc21b2396c396d88dd909caaf73d5be6ff593; version=fe881ef11cf0220f118816181930494d484c4883 <97f907203321eee2cc9132d5c9eb47698fb41d35; version=fe881ef11cf0220f118816181930494d484c4883 <c20f755338ca234e523dfc943719f194dfc1f903

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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