VulnerabilityPublished 18 Oct 2026

CVE-2026-98621: Linux kernel · net: gue: reject invalid REMCSUM offsets

Source GCVE Database

Authoritative record:CVE-2026-98621· High

Not known to be exploited · fixed in c20f755338ca234e523dfc943719f194dfc1f903 : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

Severity

High

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in c20f755338ca234e523dfc943719f194dfc1f903, 2566866fc30965d915d0b52b5c3323b362619f0e, 97f907203321eee2cc9132d5c9eb47698fb41d35 +5

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-2cjw-phmm-3745

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ fe881ef11cf0220f118816181930494d484c4883, < c20f755338ca234e523dfc943719f194dfc1f903	Fixed in c20f755338ca234e523dfc943719f194dfc1f903
LinuxLinux	Affected ≥ fe881ef11cf0220f118816181930494d484c4883, < 2566866fc30965d915d0b52b5c3323b362619f0e	Fixed in 2566866fc30965d915d0b52b5c3323b362619f0e
LinuxLinux	Affected ≥ fe881ef11cf0220f118816181930494d484c4883, < 97f907203321eee2cc9132d5c9eb47698fb41d35	Fixed in 97f907203321eee2cc9132d5c9eb47698fb41d35
LinuxLinux	Affected ≥ fe881ef11cf0220f118816181930494d484c4883, < 43efb1f997e976f386aa89716f55870cd2cff9ad	Fixed in 43efb1f997e976f386aa89716f55870cd2cff9ad
LinuxLinux	Affected ≥ fe881ef11cf0220f118816181930494d484c4883, < 40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f	Fixed in 40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f
LinuxLinux	Affected ≥ fe881ef11cf0220f118816181930494d484c4883, < 4b9bc21b2396c396d88dd909caaf73d5be6ff593	Fixed in 4b9bc21b2396c396d88dd909caaf73d5be6ff593

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AI-suggested

A fix has been implemented that rejects invalid REMCSUM offset tuples in the Linux kernel's GUE parser, preventing the underflow and subsequent buffer overflow. Users should apply the official kernel update containing this fix once available. Patch status is not explicitly confirmed in the provided data; therefore, check the vendor advisory for current remediation guidance.

Description

A vulnerability in the Linux kernel's Generic UDP Encapsulation (GUE) implementation involving the REMCSUM option has been resolved. The issue arises from an underflow in checksum offset calculations, which can lead to a buffer overflow when processing certain forwarded packets. This flaw could cause skb_copy_and_csum_dev() to write two bytes beyond the intended buffer boundary. The fix involves rejecting invalid REMCSUM offset tuples to enforce correct ordering and prevent exploitation.

Impact

The vulnerability can lead to a buffer overflow condition where two bytes are written beyond the allocated buffer boundary during packet processing. This memory corruption could potentially be exploited to cause system instability or other unintended behavior in the Linux kernel networking stack. No known exploits in the wild have been reported.

Summary

The vulnerability in the Linux kernel's GUE module relates to improper handling of the REMCSUM option's checksum start and offset fields. Specifically, gue_remcsum() passes these fields to skb_remcsum_process(), where an underflow occurs if the checksum offset is less than the start value, resulting in an incorrect skb->csum_offset. This can cause a forwarded packet with CHECKSUM_PARTIAL to reach a hardware checksum driver that trusts this metadata, leading skb_copy_and_csum_dev() to write two bytes approximately 64 KiB beyond the destination buffer, potentially causing memory corruption. The remediation involves rejecting reversed offset tuples in validate_gue_flags(), consolidating validation to prevent this underflow and subsequent buffer overflow.

References

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