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CVE-2026-89554· NVD / CVE Program· CNA Linux

mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction mptcp_token_join_cookie_init_state() restores remote_nonce, local_nonce, backup, join_id, token and msk from the saved cookie entry when rebuilding the request socket for a MP_JOIN 4th-ACK handled under SYN cookies, but it does not restore local_id, even though the SYN path saved it. subflow_ulp_clone() then reads that uninitialized field and stores it as the joined subflow's address-ID. Because the request-sock slab is SLAB_TYPESAFE_BY_RCU and not zeroed on allocation, the value is the stale byte of a previously freed request socket, which an off-path peer can influence by sending concurrent MP_JOIN SYNs. This corrupts the path manager's id-based subflow bookkeeping for the connection. Restore subflow_req->local_id from the cookie entry, as done for the other fields.

HighCVSS 8.2 · v3.1—No exploit Fix available
Published
Sep 11, 2026
Updated
Sep 14, 2026
EPSS
0.6% · 47th percentile
CWE
—
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Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.6%

CNA vs NVD score

NVD
—
CNA · Linux
8.2
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

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Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 5.9affected
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before 4534e0eead692bb069ad1e6a5a245fc2e2078300affected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before 63cacb05e51a1c6e1349d2e593d00fd6ef43def4affected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before 954b5ea836eb118d188975ced803448537ab8479affected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before 9df36a4846375a9b75bf42d77bfed216b0f366f9affected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before 64f2c5dd49b956a542c8c02b8dad5d262a462bbaaffected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before 51887ccd88791ddaa8755a7c614fda031ecf7982affected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before bf19d166337c6488b39cb03eeeffb30a941d6326affected · git
    • 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 and later · before b878dfdd12d7a5b8722a78d35e313506140ca3d9affected · git
    • before 5.9not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxall versions—
Debian:13linuxbefore 6.12.111-16.12.111-1
Debian:14linuxbefore 7.2.6-17.2.6-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan
  • CVE-2026-74309vdpa/octeon_ep: fix IRQ-to-ring mapping in interrupt handler
    40Plan
  • CVE-2026-74280crypto: marvell/octeontx - fix DMA cleanup using wrong loop index
    40Plan
  • CVE-2026-74279crypto: cavium/cpt - fix DMA cleanup using wrong loop index
    40Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux4534e0eead692bb069ad1e6a5a245fc2e2078300Vendor (CNA)
Linux Linux51887ccd88791ddaa8755a7c614fda031ecf7982Vendor (CNA)
Linux Linux63cacb05e51a1c6e1349d2e593d00fd6ef43def4Vendor (CNA)
Linux Linux64f2c5dd49b956a542c8c02b8dad5d262a462bbaVendor (CNA)
Linux Linux954b5ea836eb118d188975ced803448537ab8479Vendor (CNA)
Linux Linux9df36a4846375a9b75bf42d77bfed216b0f366f9Vendor (CNA)
Linux Linuxb878dfdd12d7a5b8722a78d35e313506140ca3d9Vendor (CNA)
Linux Linuxbf19d166337c6488b39cb03eeeffb30a941d6326Vendor (CNA)
debian:linux6.12.111-1 · Debian:13Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
low · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
Low
Availability impact
High

Weakness class (CWE)

—

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Noroxi analysis

No Noroxi analysis for this record yet

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Change log

  1. Fix✗ → ✓

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References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records