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CVE-2026-31669— mptcp: fix slab-use-after-free in __inet_lookup_established

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基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于MPTCP子流初始化时复制未注册的TCPv6协议，导致子流套接字通过kmalloc分配而非TCPv6 slab缓存，可能引发释放后重用。

CVSS 9.8 · Critical EPSS 0.84% · P57

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 16

VendorProduct Version RangeStatus
Linux Linux b19bc2945b40b9fd38e835700907ffe8534ef0de< f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47 affected
b19bc2945b40b9fd38e835700907ffe8534ef0de< fb1f54b7d16f393b8b65d328410f78b4beea8fcc affected
b19bc2945b40b9fd38e835700907ffe8534ef0de< 3fd6547f5b8ac99687be6d937a0321efda760597 affected
b19bc2945b40b9fd38e835700907ffe8534ef0de< eb9c6aeb512f877cf397deb1e4526f646c70e4a7 affected
b19bc2945b40b9fd38e835700907ffe8534ef0de< 15fa9ead4d5e6b6b9c794e84144146c917f2cb62 affected
b19bc2945b40b9fd38e835700907ffe8534ef0de< b313e9037d98c13938740e5ebda7852929366dff affected
b19bc2945b40b9fd38e835700907ffe8534ef0de< 9b55b253907e7431210483519c5ad711a37dafa1 affected
5.12 affected
… +8 more rows
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I. Basic Information for CVE-2026-31669

Vulnerability Information
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Vulnerability Title
mptcp: fix slab-use-after-free in __inet_lookup_established
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: mptcp: fix slab-use-after-free in __inet_lookup_established The ehash table lookups are lockless and rely on SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability during RCU read-side critical sections. Both tcp_prot and tcpv6_prot have their slab caches created with this flag via proto_register(). However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into tcpv6_prot_override during inet_init() (fs_initcall, level 5), before inet6_init() (module_init/device_initcall, level 6) has called proto_register(&tcpv6_prot). At that point, tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab remains NULL permanently. This causes MPTCP v6 subflow child sockets to be allocated via kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so when these sockets are freed without SOCK_RCU_FREE (which is cleared for child sockets by design), the memory can be immediately reused. Concurrent ehash lookups under rcu_read_lock can then access freed memory, triggering a slab-use-after-free in __inet_lookup_established. Fix this by splitting the IPv6-specific initialization out of mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called from mptcp_proto_v6_init() before protocol registration. This ensures tcpv6_prot_override.slab correctly inherits the SLAB_TYPESAFE_BY_RCU slab cache.
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基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于MPTCP子流初始化时复制未注册的TCPv6协议，导致子流套接字通过kmalloc分配而非TCPv6 slab缓存，可能引发释放后重用。
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)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux b19bc2945b40b9fd38e835700907ffe8534ef0de ~ f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47 -
Linux Linux 5.12 -

II. Public POCs for CVE-2026-31669

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III. Intelligence Information for CVE-2026-31669

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Same Patch Batch · Linux · 2026-04-24 · 138 CVEs total

CVE-2026-31637 9.8 CRITICAL rxrpc: reject undecryptable rxkad response tickets
CVE-2026-31536 9.8 CRITICAL smb: server: let send_done handle a completion without IB_SEND_SIGNALED
CVE-2026-31589 9.8 CRITICAL mm: call ->free_folio() directly in folio_unmap_invalidate()
CVE-2026-31668 9.8 CRITICAL seg6: separate dst_cache for input and output paths in seg6 lwtunnel
CVE-2026-31649 9.8 CRITICAL net: stmmac: fix integer underflow in chain mode
CVE-2026-31633 9.8 CRITICAL rxrpc: Fix integer overflow in rxgk_verify_response()
CVE-2026-31607 9.8 CRITICAL usbip: validate number_of_packets in usbip_pack_ret_submit()
CVE-2026-31608 9.8 CRITICAL smb: server: avoid double-free in smb_direct_free_sendmsg after smb_direct_flush_send_list
CVE-2026-31609 9.8 CRITICAL smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush()
CVE-2026-31657 9.8 CRITICAL batman-adv: hold claim backbone gateways by reference
CVE-2026-31659 9.8 CRITICAL batman-adv: reject oversized global TT response buffers
CVE-2026-31636 9.1 CRITICAL rxrpc: fix RESPONSE authenticator parser OOB read
CVE-2026-31588 8.8 HIGH KVM: x86: Use scratch field in MMIO fragment to hold small write values
CVE-2026-31570 8.8 HIGH can: gw: fix OOB heap access in cgw_csum_crc8_rel()
CVE-2026-31622 8.8 HIGH NFC: digital: Bounds check NFC-A cascade depth in SDD response handler
CVE-2026-31558 8.8 HIGH LoongArch: KVM: Make kvm_get_vcpu_by_cpuid() more robust
CVE-2026-31553 8.8 HIGH KVM: arm64: Fix the descriptor address in __kvm_at_swap_desc()
CVE-2026-31629 8.8 HIGH nfc: llcp: add missing return after LLCP_CLOSED checks
CVE-2026-31611 8.6 HIGH ksmbd: require 3 sub-authorities before reading sub_auth[2]
CVE-2026-31631 8.2 HIGH rxrpc: Fix buffer overread in rxgk_do_verify_authenticator()

Showing top 20 of 138 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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