CVE-2026-68297 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
tipc: fix u16 MTU truncation in media and bearer MTU validation
Both TIPC_NL_MEDIA_SET and TIPC_NL_BEARER_SET accept user-supplied MTU values but only enforce a minimum bound, not a maximum. When a user sets the MTU to a value exceeding U16_MAX (65535), it passes validation but is silently truncated when assigned to u16 fields l->mtu and l->advertised_mtu in tipc_link_create(). Values like 65536 (0x10000) truncate to 0, causing a division by zero in tipc_link_set_queue_limits() which computes TIPC_MAX_PUBL / (l->mtu / ITEM_SIZE). Other overflowing values (e.g. 65537-131071) produce small incorrect MTU values, resulting in link malfunction behaviors.
Crash stack (triggered as unprivileged user via user namespace):
tipc_link_set_queue_limits net/tipc/link.c:2531 tipc_link_create net/tipc/link.c:520 tipc_node_check_dest net/tipc/node.c:1279 tipc_disc_rcv net/tipc/discover.c:252 tipc_rcv net/tipc/node.c:2129 tipc_udp_recv net/tipc/udp_media.c:392
Two independent paths lack the upper bound check: 1. tipc_udp_mtu_bad() -- called from __tipc_nl_media_set() (MEDIA_SET) 2. inline check in __tipc_nl_bearer_set() at bearer.c:1160 (BEARER_SET)
Fix both by rejecting MTU values above U16_MAX.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability resides within the Linux kernel's TIPC (Transparent Inter-Process Communication) implementation where improper validation of Maximum Transmission Unit values leads to critical system instability and potential denial of service conditions. This issue affects both media and bearer MTU configuration operations through the TIPC Netlink interface, specifically targeting the TIPC_NL_MEDIA_SET and TIPC_NL_BEARER_SET commands that accept user-supplied MTU parameters without adequate upper boundary enforcement.
The technical flaw manifests in the conversion process where user-provided MTU values exceeding the u16 maximum value of 65535 are silently truncated when assigned to 16-bit fields within the tipc_link_create() function. When an MTU value of exactly 65536 is provided, it truncates to zero due to the unsigned 16-bit integer overflow, creating a division by zero condition in the tipc_link_set_queue_limits() function. This calculation involves TIPC_MAX_PUBL divided by (l->mtu / ITEM_SIZE) where the mtu field becomes zero, triggering an immediate kernel crash. Values exceeding 65535 but less than the full u16 range produce progressively smaller incorrect MTU values that result in link malfunction behaviors rather than immediate crashes.
The operational impact of this vulnerability extends beyond simple system instability to encompass complete service disruption within TIPC networks. An unprivileged user operating within a user namespace can exploit this weakness to cause kernel panics through carefully crafted MTU values, effectively creating a denial of service condition that affects the entire network communication infrastructure. The vulnerability is particularly concerning because it operates through legitimate Netlink interface mechanisms that are commonly used for network configuration management, making it difficult to distinguish between malicious and legitimate usage patterns.
The crash stack demonstrates the execution path leading to the kernel panic, showing how the validation failure propagates from user-space configuration through multiple kernel subsystems before reaching the critical division operation. The two independent code paths that lack upper bound checks represent distinct entry points for exploitation - one in tipc_udp_mtu_bad() function called during media set operations and another inline check within __tipc_nl_bearer_set() at bearer.c line 1160. This dual vulnerability surface increases the attack surface and reduces the effectiveness of any single mitigation approach.
Security implications of this vulnerability align with CWE-191 Integer Underflow/Overflow, specifically addressing integer truncation issues that occur during type conversion operations. The flaw also relates to CWE-362 Concurrent Execution using Shared Resource with Unprotected Critical Section as it involves improper validation of shared network configuration parameters. From an ATT&CK framework perspective, this represents a privilege escalation vector through local code execution and a denial of service technique leveraging kernel memory corruption patterns. The vulnerability demonstrates the importance of proper input validation in kernel space operations and highlights how seemingly benign configuration parameters can lead to critical system failures.
The recommended mitigation strategy involves implementing explicit upper bound checks that reject MTU values exceeding U16_MAX (65535) before they are processed or assigned to 16-bit fields. This fix ensures that all user-supplied MTU values are validated against both minimum and maximum boundaries, preventing the truncation that leads to division by zero conditions. The solution should be applied consistently across both identified code paths to eliminate the dual vulnerability surface and ensure comprehensive protection of the TIPC subsystem. Additionally, system administrators should monitor for any unauthorized configuration changes to TIPC network parameters and implement proper access controls to limit the potential attack vectors.