CVE-2026-89554Network attack vector

MPTCP subflow bookkeeping corruption via uninitialized address ID

Published Sep 11, 2026 · Updated Sep 11, 2026

Uninitialized state in Linux allows remote attackers to corrupt MPTCP subflow bookkeeping through concurrent MP_JOIN traffic. mptcp_token_join_cookie_init_state() fails to restore the saved local_id, and subflow_ulp_clone() consequently copies a stale request-socket slab byte into the joined subflow's address ID. Reachability requires an existing MPTCP connection that accepts new subflows and handles MP_JOIN under SYN cookies; the bounded consequence is corrupted path-manager bookkeeping.

CVSS severityUnavailable
Unscored
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uninitialized state in Linux allows remote attackers to corrupt MPTCP subflow bookkeeping through concurrent MP_JOIN traffic. mptcp_token_join_cookie_init_state() fails to restore the saved local_id, and subflow_ulp_clone() consequently copies a stale request-socket slab byte into the joined subflow's address ID. Reachability requires an existing MPTCP connection that accepts new subflows and handles MP_JOIN under SYN cookies; the bounded consequence is corrupted path-manager bookkeeping.

The record

CVE
CVE-2026-89554
Published
Sep 11, 2026
Updated
Sep 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 11, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 11, 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=5.9
  2. Affected versionversion=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <51887ccd88791ddaa8755a7c614fda031ecf7982
  3. Affected versionversion=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <64f2c5dd49b956a542c8c02b8dad5d262a462bba
  4. Affected versionversion=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <b878dfdd12d7a5b8722a78d35e313506140ca3d9
  5. Affected versionversion=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <bf19d166337c6488b39cb03eeeffb30a941d6326

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.9; version=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <51887ccd88791ddaa8755a7c614fda031ecf7982; version=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <64f2c5dd49b956a542c8c02b8dad5d262a462bba; version=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <b878dfdd12d7a5b8722a78d35e313506140ca3d9; version=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <bf19d166337c6488b39cb03eeeffb30a941d6326

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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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