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CVE-2026-80587— mptcp: avoid combining some incoming suboptions

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel 5.6版本存在安全漏洞，该漏洞源于MPTCP对传入子选项的组合处理不当，未能正确识别互斥选项，可能导致远程攻击者利用特制MPTCP子选项造成数据泄露、连接状态损坏或拒绝服务。

CVSS 9.8 · Critical EPSS 0.40% · P33

Possible ATT&CK Techniques 1 AI

T1213 · Data from Information Repositories

Affected Version Matrix 14

VendorProduct Version RangeStatus
Linux Linux eda7acddf8080bb2d022a8d4b8b2345eb80c63ec< 0e2210af439755a2af352eea4178261dcf61742e affected
eda7acddf8080bb2d022a8d4b8b2345eb80c63ec< dc1d8d3eb345c616fbe922a010fa391c72c54d52 affected
eda7acddf8080bb2d022a8d4b8b2345eb80c63ec< 099bfcbd0c16ae9b50aba2a1bea033e63f895da7 affected
eda7acddf8080bb2d022a8d4b8b2345eb80c63ec< a04dcc784959e4702048785d87e0d029bd2fbdcb affected
eda7acddf8080bb2d022a8d4b8b2345eb80c63ec< 6bab907292155513af397a12ccb488acbfc30d79 affected
eda7acddf8080bb2d022a8d4b8b2345eb80c63ec< b6ee361524641f57b2e2363f7737f20e17f67827 affected
5.6 affected
< 5.6 unaffected
… +6 more rows
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I. Basic Information for CVE-2026-80587

Vulnerability Information
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Vulnerability Title
mptcp: avoid combining some incoming suboptions
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel 5.6版本存在安全漏洞，该漏洞源于MPTCP对传入子选项的组合处理不当，未能正确识别互斥选项，可能导致远程攻击者利用特制MPTCP子选项造成数据泄露、连接状态损坏或拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux eda7acddf8080bb2d022a8d4b8b2345eb80c63ec ~ 0e2210af439755a2af352eea4178261dcf61742e -
Linux Linux 5.6 -

II. Public POCs for CVE-2026-80587

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III. Intelligence Information for CVE-2026-80587

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Patches & Fixes for CVE-2026-80587 (5)

Other References for CVE-2026-80587 (1)

Same Patch Batch · Linux · 2026-08-26 · 92 CVEs total

CVE-2026-80589 9.8 CRITICAL block: stop the timeout timer when releasing a never added disk
CVE-2026-74752 9.8 CRITICAL sctp: validate cookie AUTH state before use
CVE-2026-80519 9.8 CRITICAL ovpn: finish crypto callback cleanup before peer release
CVE-2026-74746 9.8 CRITICAL netfilter: flowtable: publish GC-visible tuple last
CVE-2026-80528 9.8 CRITICAL ceph: avoid fs reclaim while using current->journal_info
CVE-2026-74744 9.8 CRITICAL ipvlan: inherit needed_headroom and needed_tailroom from phy_dev
CVE-2026-74743 9.8 CRITICAL macvlan: inherit needed_headroom and needed_tailroom from lowerdev
CVE-2026-80561 9.8 CRITICAL libceph: fix multiple unsafe decodes in decode_locker()
CVE-2026-80558 9.8 CRITICAL libceph: Avoid using invalid osd indices from primary_temp
CVE-2026-80586 9.8 CRITICAL mptcp: options: reset DSS fields in case of unexpected size
CVE-2026-80557 9.8 CRITICAL libceph: fix OOB read in decode_watchers() via missing bounds check
CVE-2026-74737 9.8 CRITICAL net: ethernet: ti: am65-cpsw-nuss: Fix port_id extraction from SRC TAG
CVE-2026-80585 9.4 CRITICAL mptcp: fastopen: only mark MPTFO subflows with SYN data
CVE-2026-74751 9.4 CRITICAL riscv: lib: Fix ZBB strnlen reading past count boundary
CVE-2026-80554 9.3 CRITICAL s390/vfio_ccw: Limit the number of channel program segments
CVE-2026-80551 9.3 CRITICAL s390/vfio_ccw: Ensure first IDAW remains constant
CVE-2026-80547 8.8 HIGH s390/vfio_ccw: Implement a crw lock
CVE-2026-80576 8.8 HIGH drm/amdgpu: reject oversized IBs with per-ring packet limits
CVE-2026-80552 8.8 HIGH s390/vfio_ccw: Ensure index for read/write regions are within range
CVE-2026-80553 8.8 HIGH s390/vfio_ccw: Cancel existing workqueues

Showing top 20 of 92 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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