CVE-2026-80587
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, e
CSIRTS triage
- What
- The MPTCP subsystem fails to properly handle certain incoming suboptions, potentially causing denial of service.
- Who is affected
- Systems running Linux kernel versions with MPTCP support enabled.
- Urgency
- Medium severity (CVSS 5.3); not currently exploited but should be patched in routine updates.
- Action
- Apply kernel security patch addressing CVE-2026-80587 when available from your distribution.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.39% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 32% of all EPSS-scored CVEs.
Advisory coverage (2)
- criticalCVE-2026-80587: In the Linux kernel, the following vulnerability has been resolved: mptcp: avoid combining som…nvd · 2026-08-26
- mediumCVE-2026-80587: mptcp: avoid combining some incoming suboptionsmsrc · 2026-08-11
External references
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