CVE-2026-64450 in Linux
Summary
by MITRE • 07/25/2026
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.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability described represents a critical out-of-bounds read condition within the Linux kernel's TIPC (Transparent Inter-Process Communication) implementation, specifically affecting the broadcast Gap ACK block handling mechanism. This flaw exists in the tipc_link_advance_transmq() function where it processes broadcast PROTOCOL/STATE_MSG messages containing Gap ACK blocks without proper bounds checking against the actual message data area size. The issue stems from inconsistent validation between unicast and broadcast code paths, with the unicast handler properly bounding the record size while the broadcast handler neglects this crucial check.
The technical exploitation of this vulnerability occurs when a malicious TIPC neighbor negotiates TIPC_GAP_ACK_BLOCK capability and sends a specially crafted broadcast STATE_MSG message. The attacker constructs a message where the data area is intentionally short but contains a Gap ACK record with a large len field value of 0x400, bgack_cnt set to 0xff, and ugack_cnt set to 0. This configuration causes the consistency check to pass because sz == struct_size(p, gacks, ugack_cnt + bgack_cnt) evaluates to 1024 bytes, but the actual message data area is much smaller. The kernel then performs a kmemdup() operation that reads 1024 bytes from an off-the-bounds memory region, triggering a KASAN slab-out-of-bounds error as demonstrated in the crash trace.
This vulnerability directly maps to CWE-129: Improper Validation of Array Index and CWE-787: Out-of-Bounds Write, with implications for the ATT&CK technique T1059.001: Command and Scripting Interpreter - PowerShell and similar execution methods that could leverage such memory corruption for privilege escalation or system compromise. The flaw affects the kernel's memory safety mechanisms and could potentially enable attackers to gain arbitrary code execution by corrupting kernel memory, particularly through the use of controlled data structures that get copied beyond their allocated boundaries.
The operational impact of this vulnerability extends beyond immediate memory corruption as it represents a potential vector for privilege escalation attacks against systems running TIPC networks. Systems utilizing TIPC for inter-process communication, cluster networking, or telecommunications infrastructure become vulnerable to remote exploitation by adversaries who can craft malicious broadcast messages to trigger the out-of-bounds read condition. The fix implemented addresses this by ensuring consistent validation across both unicast and broadcast code paths through proper bounds checking in tipc_bcast_sync_rcv() that compares the Gap ACK record size against msg_data_sz(), and subsequently discards the message if it exceeds the available data area.
The mitigation strategy involves implementing proper bounds validation in the broadcast processing path, similar to the existing unicast validation logic. This ensures that when a Gap ACK block record exceeds the available message data area, the entire message is discarded rather than processed, preventing the out-of-bounds memory read from occurring. The solution maintains the legitimate behavior where ga == NULL indicates a legacy peer without Selective ACK capability while ensuring that malformed messages are properly rejected at the protocol level. This approach aligns with defensive programming practices and security-by-design principles that prevent resource exhaustion attacks and maintain kernel memory integrity during message processing operations. The fix represents a typical remediation for buffer over-read vulnerabilities in kernel networking code and demonstrates the importance of consistent validation across all execution paths within complex protocol implementations.