CVE-2026-80587 — mptcp: avoid combining some incoming suboptions
In 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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- Technical severity (critical)+10
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux | ≥ eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and < 0e2210af439755a2af352eea4178261dcf61742e≥ eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and < dc1d8d3eb345c616fbe922a010fa391c72c54d52≥ eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and < 099bfcbd0c16ae9b50aba2a1bea033e63f895da7≥ eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and < a04dcc784959e4702048785d87e0d029bd2fbdcb≥ eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and < 6bab907292155513af397a12ccb488acbfc30d79≥ eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and < b6ee361524641f57b2e2363f7737f20e17f67827version 5.6 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 9.8 | CVSS 3.1 | Critical | 3.9 | 5.9 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database |
| 9.8 | CVSS 3.1 | Critical | — | — | Linux via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- CVSS changed · 9.8
- Source status changed · → Received
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 15, 2026 – Oct 15, 2026
References
6 on the record
- git.kernel.org/stable/c/6bab907292155513af397a12ccb488acbfc30d79
- git.kernel.org/stable/c/b6ee361524641f57b2e2363f7737f20e17f67827
- git.kernel.org/stable/c/a04dcc784959e4702048785d87e0d029bd2fbdcb
- git.kernel.org/stable/c/099bfcbd0c16ae9b50aba2a1bea033e63f895da7
- git.kernel.org/stable/c/dc1d8d3eb345c616fbe922a010fa391c72c54d52
- git.kernel.org/stable/c/0e2210af439755a2af352eea4178261dcf61742e
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 14h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 14h
- Unknown CVE-2026-98430 RDMA/efa: Keep admin queues alive while IRQ is registered 1d
- Unknown CVE-2026-98431 RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency 1d
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No FIRST EPSS score.
- No fixed version, patch or mitigation documented.
- No CISA SSVC assessment.
- No CWE classification.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-80587 is "mptcp: avoid combining some incoming suboptions", rated Critical. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.8 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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