CVE-2026-80587
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk29th percentile - higher than 29% of all known CVEs
Summary
In the Linux kernel's MPTCP module, a vulnerability was found due to lack of rejection of mutually exclusive incoming MPTCP suboptions. An attacker can send a packet with a combination of suboptions that according to RFC 8684 cannot coexist, potentially leading to unexpected network stack behavior. The fix introduces validation consistent with outgoing rules, ignoring invalid combinations.
Risk Assessment
The risk involves potential destabilization of the MPTCP stack by a remote attacker, which could lead to network service errors or denial of service (DoS). Lack of validation may also allow bypassing security measures relying on suboption combination restrictions.
Recommendation
It is recommended to apply the kernel patch containing this fix as soon as possible. Update the system to a kernel version with the patch and monitor security advisories for new versions.
Other vulnerabilities in Linux kernel
See all- CVE-2026-98374Unknown
In the Linux kernel, a use-after-free vulnerability exists in tcp_send_synack() involving retransmit_skb_hint. When tcp_send_synack() replaces the cloned SYN skb at the head of the retransmit queue with a copy, it frees the original but tp->retransmit_skb_hint still points to the freed object, which can be exploited by an unprivileged TFO client to trigger a use-after-free.
- CVE-2026-98373Unknown
In the Linux kernel, a bug exists in move_hugetlb_page_tables() where the destination address is advanced too far when the source and destination offsets within their page tables differ. This can lead to a kernel panic on x86-64.
- CVE-2026-98048Unknown
In the Linux kernel's BPF subsystem, mark_fastcall_pattern_for_call() must ensure that a matched "spill; call; fill" instruction series is not interrupted by a jump. Otherwise the rewrite applied by bpf_remove_fastcall_spills_fills() is unsound. The fix records instructions targeted by jumps in insn_aux_data[*].jump_target and uses this flag to stop growing a pattern.
- CVE-2026-98047Unknown
In the Linux kernel's BPF subsystem, in_rbtree_lock_required_cb() only checks the innermost verifier frame, so rbtree callback restrictions disappear in a nested static subprogram call frame. The subprogram can unlock the tree, remove and drop the node being compared, then relock, leading to freed memory being linked into the tree.
- CVE-2026-98045Unknown
In the Linux kernel, a BPF verifier vulnerability affects stack helpers that may block on filesystem reads (e.g., resolving build IDs) but were not marked as sleepable. The verifier could still allow these helpers from non-sleepable regions such as RCU or preemption-disabled sections.
- CVE-2026-98044Unknown
In the Linux kernel, the BPF verifier mishandled legacy packet-load instructions (BPF_LD_ABS/BPF_LD_IND) reached from callbacks, triggering a verifier bug warning and an -EFAULT on BPF_PROG_LOAD. A privileged program loader could trigger this issue.
- CVE-2026-98043Unknown
In the Linux kernel, the BPF verifier incorrectly inferred that a pointer with an unbounded offset is non-NULL based solely on its type. As a result, a BPF program could pass verification while a NULL pointer dereference occurred at runtime.
- CVE-2026-98042Unknown
In the Linux kernel, the BPF verifier could resurrect a scalar id dropped by collect_linked_regs() because snapshots of compared registers were taken before linked registers were collected. This could lead to range inconsistencies and precision propagation issues.
- CVE-2026-98041High
In the Linux kernel, the BPF verifier incorrectly predicted the outcome of pointer vs zero comparisons in JMP32 instructions, failing to distinguish BPF_JMP from BPF_JMP32 comparisons. This led to incorrect inference that a jump is always taken.
- CVE-2026-98040Unknown
In the Linux kernel, the BPF verifier did not mark the zero register as precise for a register-form NULL check. As a result, one path was pruned and the program could dereference a zero pointer at runtime.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS