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CVE-2026-80842— net: bridge: mcast: fix use-after-free of a master VLAN's multicast context

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存在安全漏洞，该漏洞源于主VLAN的多播上下文存在释放后重用问题，可能导致系统崩溃或内存破坏。

AI Predicted 5.7 Difficulty: Hard EPSS 0.18% · P7

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 7b54aaaf53cb784411426c64482af0435f7c845e< 3afaaee2f972aec9059110953adb62fa3cf5c4bd affected
7b54aaaf53cb784411426c64482af0435f7c845e< 22226a2c3b90f15b0925f1464470d3baa6c5677e affected
7b54aaaf53cb784411426c64482af0435f7c845e< 7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686 affected
7b54aaaf53cb784411426c64482af0435f7c845e< 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50 affected
7b54aaaf53cb784411426c64482af0435f7c845e< c069f29da72324697aa4b7cab5b3647a7d24a575 affected
7b54aaaf53cb784411426c64482af0435f7c845e< 3f4752996735e0628af559aa8da1d872c2fac13b affected
7b54aaaf53cb784411426c64482af0435f7c845e< 57f94d3f4dee8b54d63cefddf1112be4656ef9e6 affected
7b54aaaf53cb784411426c64482af0435f7c845e< 50e5c6605cc9c2dd57bd2d1b3459674d19738983 affected
… +10 more rows
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I. Basic Information for CVE-2026-80842

Vulnerability Information
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Vulnerability Title
net: bridge: mcast: fix use-after-free of a master VLAN's multicast context
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: net: bridge: mcast: fix use-after-free of a master VLAN's multicast context br_multicast_toggle_one_vlan() clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before stopping a VLAN's multicast context. That is the teardown handshake: lockless readers gate on the flag through br_multicast_ctx_should_use() -> br_multicast_ctx_vlan_disabled(), so once it is cleared under the lock no reader can arm the context again. For a master VLAN the handshake never runs. __vlan_del() clears BRIDGE_VLAN_INFO_BRENTRY before calling br_vlan_put_master(), so br_multicast_toggle_one_vlan(masterv, false) returns early on !br_vlan_is_brentry(vlan): the flag stays set and br->multicast_lock is never taken. br_vlan_put_master() then drains the context in br_multicast_ctx_deinit() and frees the VLAN through call_rcu(), while a reader still inside rcu_read_lock() sees the context as enabled and re-arms it. The port and port-VLAN branch of the function has no br_vlan_is_brentry() test and flips the flag under br->multicast_lock, so it is not affected. The reader is the bridge transmit path. For a master VLAN br_multicast_rcv() selects brmctx = &vlan->br_mcast_ctx with pmctx = NULL, so IGMP sent to the bridge device re-arms the context's timers after br_multicast_ctx_deinit() has already stopped them. BUG: KASAN: slab-use-after-free in detach_if_pending+0x412/0x4a0 Write of size 8 at addr ffff88810ac39918 by task brmc/601 __mod_timer+0x51a/0xc50 br_multicast_host_join+0x25b/0x390 __br_multicast_add_group+0x468/0x530 br_ip4_multicast_add_group+0x1a0/0x260 br_multicast_rcv+0x2cda/0x61e0 br_dev_xmit+0x6c4/0x1540 Allocated by task 610: br_vlan_add+0x111/0xb40 br_vlan_info+0x370/0x3e0 Freed by task 0: kfree+0x1a7/0x4f0 rcu_core+0x7dc/0x10a0 Only test br_vlan_is_brentry() when enabling, like the br_multicast_ctx_vlan_global_disabled() test next to it. Disabling then always clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before br_multicast_ctx_deinit() drains the context.
Source: CVE Program / CVE List V5
CVSS Information
N/A
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存在安全漏洞，该漏洞源于主VLAN的多播上下文存在释放后重用问题，可能导致系统崩溃或内存破坏。
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 7b54aaaf53cb784411426c64482af0435f7c845e ~ 3afaaee2f972aec9059110953adb62fa3cf5c4bd -
Linux Linux 5.15 -

II. Public POCs for CVE-2026-80842

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III. Intelligence Information for CVE-2026-80842

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Patches & Fixes for CVE-2026-80842 (7)

Same Patch Batch · Linux · 2026-09-04 · 156 CVEs total

CVE-2026-80865 bpf: Add missing access_ok call to copy_user_syms
CVE-2026-80856 fuse: fix invalidate lock leak on setattr writeback failure
CVE-2026-80857 fuse: wait for FR_FINISHED on abort_on_kill to prevent use-after-free
CVE-2026-80858 fuse: publish io-uring queues with release semantics
CVE-2026-80859 fuse: fix missing barrier when checking io-uring readiness
CVE-2026-80860 fuse: fix race between interrupt and resend
CVE-2026-80861 usb: xhci: bail out of setup if the controller is inaccessible
CVE-2026-80862 nvme-tcp: fix usage of page_frag_cache
CVE-2026-80863 RDMA/rxe: Fix OOB in free_rd_atomic_resources()
CVE-2026-80864 RDMA/rxe: Fix responder UAF on IB_QP_MAX_DEST_RD_ATOMIC modify_qp
CVE-2026-80870 drm/amdkfd: Validate CRIU-restored IDs before idr_alloc
CVE-2026-80874 arm64: dts: renesas: ironhide: Describe inline ECC carveouts
CVE-2026-80873 KVM: arm64: nv: Write ESR_EL2 for injected nested SError exceptions
CVE-2026-80872 ALSA: hda/tas2781: Cancel async firmware request at unbind
CVE-2026-80871 crypto: xilinx-trng - Remove crypto_rng interface
CVE-2026-80868 ntfs3: Allocate iomap inline_data using alloc_page
CVE-2026-80866 tipc: avoid busy looping in tipc_exit_net()
CVE-2026-80867 alpha/PCI: Add security_locked_down() check to pci_mmap_resource()
CVE-2026-80855 fuse: fix invalidate lock leak on open O_TRUNC DAX failure
CVE-2026-80869 ntfs: bound the attribute-list entry in ntfs_read_inode_mount()

Showing top 20 of 156 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-80842

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