mptcp: avoid combining some incoming suboptions

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-80587
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-26 15:17:15 UTC
Updated2026-08-27 13:18:41 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: mptcp: avoid combining some incoming suboptions Some MPTCP suboptions are mutually exclusive according to the RFC8684, but also because in different places, the code doesn't expect some combinations to be present. That's specially true for suboptions that would be present twice, but with different attributes. The new restrictions are the same as the ones applied on the output side, with mptcp_write_options. The same rules can be reused with a small fix: an MP_FASTCLOSE can be used with a DSS when the sender picks this option [1], which is not the case on Linux. Here are the rules: Which options can be used together? X: mutually exclusive O: often used together C: can be used together in some cases P: could be used together but we prefer not to (optimisations) | Opt: | MPC | MPJ | DSS | ADD | RM | PRIO | FAIL | FC | |------|------|------|------|------|------|------|------|------| | MPC |------|------|------|------|------|------|------|------| | MPJ | X |------|------|------|------|------|------|------| | DSS | X | X |------|------|------|------|------|------| | ADD | X | X | P |------|------|------|------|------| | RM | C | C | C | P |------|------|------|------| | PRIO | X | C | C | C | C |------|------|------| | FAIL | X | X | C | X | X | X |------|------| | FC | X | X | P | X | X | X | X |------| | RST | X | X | X | X | X | X | O | O | |------|------|------|------|------|------|------|------|------| The only difference is with the 'P': another stack could send and ADD_ADDR with other suboptions (DSS, RM_ADDR), and this should be allowed. A few points of attention: - In theory, an MP_CAPABLE could be used with a RM_ADDR, but there is no reason to add it with a SYN. Note that even with a 4th ACK, it doesn't seem to be useful, except when IDs are known in advance via another channel. Better not to break that. - Now, combining both an MP_CAPABLE and an MP_JOIN will no longer result to a reject of the two options, but only the second suboption is ignored. That seems OK to do that for this unexpected error. At least now all inconsistent combinations are handled the same way. This could change later in next. This also means the explicit checks for having both MPC + MPJ in subflow.c will now be unreachable. That's fine, they will be removed in a follow-up patch. - In case of conflicting combinations, the extra suboption(s) is/are ignored: having such combinations either means the remote peer is buggy, or is evil. The simplest action is then taken in this case: stop processing the current suboption. - In mp_opt->suboptions, there is also a bit reserved to the checksum, which can be used in an MP_CAPABLE and a DSS. Each time a DSS option can be used in parallel with another option, the checksum can be set, so the verification is combined into a new OPTIONS_MPTCP_DSS macro. - An MP_CAPABLE ACK can carry a Data-Level Length, and an optional Checksum: they are the same as the ones found in a DSS, because a DSS cannot be used in parallel to an MP_CAPABLE. Similarly, even if there is room, a DSS cannot be used with an MP_JOIN.

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.003640000 probability, percentile 0.291710000 (date 2026-08-27)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected eda7acddf8080bb2d022a8d4b8b2345eb80c63ec 0e2210af439755a2af352eea4178261dcf61742e git Not specified
CNA Linux Linux affected eda7acddf8080bb2d022a8d4b8b2345eb80c63ec dc1d8d3eb345c616fbe922a010fa391c72c54d52 git Not specified
CNA Linux Linux affected eda7acddf8080bb2d022a8d4b8b2345eb80c63ec 099bfcbd0c16ae9b50aba2a1bea033e63f895da7 git Not specified
CNA Linux Linux affected eda7acddf8080bb2d022a8d4b8b2345eb80c63ec a04dcc784959e4702048785d87e0d029bd2fbdcb git Not specified
CNA Linux Linux affected eda7acddf8080bb2d022a8d4b8b2345eb80c63ec 6bab907292155513af397a12ccb488acbfc30d79 git Not specified
CNA Linux Linux affected eda7acddf8080bb2d022a8d4b8b2345eb80c63ec b6ee361524641f57b2e2363f7737f20e17f67827 git Not specified
CNA Linux Linux affected 5.6 Not specified
CNA Linux Linux unaffected 5.6 semver Not specified
CNA Linux Linux unaffected 5.15.218 5.15.* semver Not specified
CNA Linux Linux unaffected 6.6.153 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.105 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.46 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.10 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0e2210af439755a2af352eea4178261dcf61742e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a04dcc784959e4702048785d87e0d029bd2fbdcb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6bab907292155513af397a12ccb488acbfc30d79 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/099bfcbd0c16ae9b50aba2a1bea033e63f895da7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/dc1d8d3eb345c616fbe922a010fa391c72c54d52 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b6ee361524641f57b2e2363f7737f20e17f67827 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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