CVE-2026-98255Public exploitNetwork attack vector

TCP receive-state advancement via stale-ACK validation bypass

Published Oct 6, 2026 · Updated Oct 6, 2026

Improper TCP segment validation in the Linux kernel allows remote attackers to advance receive state with data carrying an excessively old ACK. In tcp_rcv_established(), header prediction processes payload before tcp_ack() rejects the stale ACK, so RCV.NXT advances instead of the segment being discarded. The published test uses an established connection and correctly sequenced payload; it does not establish off-path injection or application-level compromise.

CVSS severityUnavailable
Unscored
EPSS probability0.18%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper TCP segment validation in the Linux kernel allows remote attackers to advance receive state with data carrying an excessively old ACK. In tcp_rcv_established(), header prediction processes payload before tcp_ack() rejects the stale ACK, so RCV.NXT advances instead of the segment being discarded. The published test uses an established connection and correctly sequenced payload; it does not establish off-path injection or application-level compromise.

The record

CVE
CVE-2026-98255
Published
Oct 6, 2026
Updated
Oct 6, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 6, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

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.

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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 exploitPublished

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

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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