GHSA-J9HG-J7Q4-CHJV
Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-27 06:30In 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": [],
"aliases": [
"CVE-2026-64450"
],
"database_specific": {
"cwe_ids": [
"CWE-125"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-25T10:17:29Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix out-of-bounds read in broadcast Gap ACK blocks\n\nA broadcast PROTOCOL/STATE_MSG can carry a Gap ACK blocks record in its\ndata area. tipc_get_gap_ack_blks() only verifies that the record\u0027s len\nfield is self-consistent with its ugack_cnt/bgack_cnt counts\n(sz == struct_size(p, gacks, ugack_cnt + bgack_cnt)); it does not check\nthat the record actually fits in the message data area, msg_data_sz().\n\nThe unicast caller tipc_link_proto_rcv() bounds it (\"if (glen \u003e dlen)\nbreak;\"), but the broadcast caller tipc_bcast_sync_rcv() discards the\nreturned size, so tipc_link_advance_transmq() copies the record off the\nreceive skb with an attacker-controlled count:\n\n\tthis_ga = kmemdup(ga, struct_size(ga, gacks, ga-\u003ebgack_cnt),\n\t\t\t GFP_ATOMIC);\n\nA TIPC neighbour that negotiated TIPC_GAP_ACK_BLOCK triggers it with one\nordinary broadcast STATE_MSG (msg_bc_ack_invalid() clear), sized so its\ndata area is short, carrying a Gap ACK record with len = 0x400,\nbgack_cnt = 0xff and ugack_cnt = 0. len then equals\nstruct_size(p, gacks, 255), so the consistency check passes and ga is\nnon-NULL; kmemdup() reads struct_size(ga, gacks, 255) = 1024 bytes out\nof the much smaller skb:\n\n BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x48/0x60\n Read of size 1024 at addr ffff0000c7030d38 by task poc864/69\n Call trace:\n kmemdup_noprof+0x48/0x60\n tipc_link_advance_transmq+0x86c/0xb80\n tipc_link_bc_ack_rcv+0x19c/0x1e0\n tipc_bcast_sync_rcv+0x1c4/0x2c4\n tipc_rcv+0x85c/0x1340\n tipc_l2_rcv_msg+0xac/0x104\n The buggy address belongs to the object at ffff0000c7030d00\n which belongs to the cache skbuff_small_head of size 704\n The buggy address is located 56 bytes inside of\n allocated 704-byte region [ffff0000c7030d00, ffff0000c7030fc0)\n\nThe copied-out bytes are subsequently consumed as gap/ack values, but\nthe read is already out of bounds at the kmemdup() regardless of how\nthey are used.\n\nThe unicast STATE path drops such a message: \"if (glen \u003e dlen) break;\"\nskips the rest of STATE_MSG handling and the skb is freed. Make the\nbroadcast path drop it too. tipc_bcast_sync_rcv() now bounds the record\nagainst msg_data_sz() and, when it does not fit, reports it back through\ntipc_node_bc_sync_rcv() to tipc_rcv() so the skb is discarded rather than\nprocessed. ga is not cleared on this path: ga == NULL already means\n\"legacy peer without Selective ACK\", a distinct legitimate state.",
"id": "GHSA-j9hg-j7q4-chjv",
"modified": "2026-07-27T06:30:38Z",
"published": "2026-07-25T12:31:36Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64450"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/016f5995c37a5a2c45198308f830f244517d70b7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/055663d21dc4336f67933ab26bef3c5934be6324"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2b66974a1b6134a4bbc3bfed181f7418f688eb54"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2de42e268174766cb2e2b90721afdfdff70e0d8d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/74b45af86a767594ba52330cd440ea84e24d700d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9a51115fcdc78687c8852bf93a1db3951dbb223b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a21ed5064217cc33726da6c7ef1a520eba43aea1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f333b6851bdf326fd2134133272dbbed0c94d921"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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