---
id: CVE-2026-64450
title: 'tipc: fix out-of-bounds read in broadcast Gap ACK blocks'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tipc: fix out-of-bounds read in broadcast Gap ACK blocks

  A broadcast PROTOCOL/STATE_MSG can carry a Gap ACK blocks record in its
  data area. tipc_get_gap_ack_blks() onl…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    055663d21dc4336f67933ab26bef3c5934be6324
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    016f5995c37a5a2c45198308f830f244517d70b7
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    74b45af86a767594ba52330cd440ea84e24d700d
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    9a51115fcdc78687c8852bf93a1db3951dbb223b
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    a21ed5064217cc33726da6c7ef1a520eba43aea1
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    2de42e268174766cb2e2b90721afdfdff70e0d8d
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    f333b6851bdf326fd2134133272dbbed0c94d921
  - >-
    Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa <
    2b66974a1b6134a4bbc3bfed181f7418f688eb54
  - Linux 5.8
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-16T15:41:04.841993Z'
published: '2026-07-25'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:42:37.192Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-64450'
references:
  - url: 'https://git.kernel.org/stable/c/055663d21dc4336f67933ab26bef3c5934be6324'
  - url: 'https://git.kernel.org/stable/c/016f5995c37a5a2c45198308f830f244517d70b7'
  - url: 'https://git.kernel.org/stable/c/74b45af86a767594ba52330cd440ea84e24d700d'
  - url: 'https://git.kernel.org/stable/c/9a51115fcdc78687c8852bf93a1db3951dbb223b'
  - url: 'https://git.kernel.org/stable/c/a21ed5064217cc33726da6c7ef1a520eba43aea1'
  - url: 'https://git.kernel.org/stable/c/2de42e268174766cb2e2b90721afdfdff70e0d8d'
  - url: 'https://git.kernel.org/stable/c/f333b6851bdf326fd2134133272dbbed0c94d921'
  - url: 'https://git.kernel.org/stable/c/2b66974a1b6134a4bbc3bfed181f7418f688eb54'
tags:
  - cve.org
epss: 0.00537
epssPercentile: 0.44003
ingestedAt: '2026-10-16T17:24:46.822Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

tipc: fix out-of-bounds read in broadcast Gap ACK blocks

A broadcast PROTOCOL/STATE_MSG can carry a Gap ACK blocks record in its
data area. tipc_get_gap_ack_blks() only verifies that the record's len
field is self-consistent with its ugack_cnt/bgack_cnt counts
(sz == struct_size(p, gacks, ugack_cnt + bgack_cnt)); it does not check
that the record actually fits in the message data area, msg_data_sz().

The unicast caller tipc_link_proto_rcv() bounds it ("if (glen > dlen)
break;"), but the broadcast caller tipc_bcast_sync_rcv() discards the
returned size, so tipc_link_advance_transmq() copies the record off the
receive skb with an attacker-controlled count:

	this_ga = kmemdup(ga, struct_size(ga, gacks, ga->bgack_cnt),
			  GFP_ATOMIC);

A TIPC neighbour that negotiated TIPC_GAP_ACK_BLOCK triggers it with one
ordinary broadcast STATE_MSG (msg_bc_ack_invalid() clear), sized so its
data area is short, carrying a Gap ACK record with len = 0x400,
bgack_cnt = 0xff and ugack_cnt = 0. len then equals
struct_size(p, gacks, 255), so the consistency check passes and ga is
non-NULL; kmemdup() reads struct_size(ga, gacks, 255) = 1024 bytes out
of the much smaller skb:

  BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x48/0x60
  Read of size 1024 at addr ffff0000c7030d38 by task poc864/69
  Call trace:
   kmemdup_noprof+0x48/0x60
   tipc_link_advance_transmq+0x86c/0xb80
   tipc_link_bc_ack_rcv+0x19c/0x1e0
   tipc_bcast_sync_rcv+0x1c4/0x2c4
   tipc_rcv+0x85c/0x1340
   tipc_l2_rcv_msg+0xac/0x104
  The buggy address belongs to the object at ffff0000c7030d00
   which belongs to the cache skbuff_small_head of size 704
  The buggy address is located 56 bytes inside of
   allocated 704-byte region [ffff0000c7030d00, ffff0000c7030fc0)

The copied-out bytes are subsequently consumed as gap/ack values, but
the read is already out of bounds at the kmemdup() regardless of how
they are used.

The unicast STATE path drops such a message: "if (glen > dlen) break;"
skips the rest of STATE_MSG handling and the skb is freed. Make the
broadcast path drop it too. tipc_bcast_sync_rcv() now bounds the record
against msg_data_sz() and, when it does not fit, reports it back through
tipc_node_bc_sync_rcv() to tipc_rcv() so the skb is discarded rather than
processed. ga is not cleared on this path: ga == NULL already means
"legacy peer without Selective ACK", a distinct legitimate state.

## Affected

- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 055663d21dc4336f67933ab26bef3c5934be6324`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 016f5995c37a5a2c45198308f830f244517d70b7`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 74b45af86a767594ba52330cd440ea84e24d700d`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 9a51115fcdc78687c8852bf93a1db3951dbb223b`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < a21ed5064217cc33726da6c7ef1a520eba43aea1`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 2de42e268174766cb2e2b90721afdfdff70e0d8d`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < f333b6851bdf326fd2134133272dbbed0c94d921`
- `Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 2b66974a1b6134a4bbc3bfed181f7418f688eb54`
- `Linux 5.8`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.