UBUNTU-CVE-2026-68297: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: tipc: fix u16 MTU truncation in media and bearer MTU validation Both TIPCNLMEDIASET and TIPCNLBEARERSET accept user-supplied MTU values but only enforce a minimum bound, not a maximum. When a user sets the MTU to a value exceeding U16MAX (65535), it passes validation but is silently truncated when assigned to u16 fields l->mtu and l->advertisedmtu in tipclinkcreate(). Values like 65536 (0x10000) truncate to 0, causing a division by zero in tipclinksetqueuelimits() which computes TIPCMAXPUBL / (l->mtu / ITEMSIZE). 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): tipclinksetqueuelimits net/tipc/link.c:2531 tipclinkcreate net/tipc/link.c:520 tipcnodecheckdest net/tipc/node.c:1279 tipcdiscrcv net/tipc/discover.c:252 tipcrcv net/tipc/node.c:2129 tipcudprecv net/tipc/udpmedia.c:392 Two independent paths lack the upper bound check: 1. tipcudpmtubad() -- called from tipcnlmediaset() (MEDIASET) 2. inline check in tipcnlbearerset() at bearer.c:1160 (BEARERSET) Fix both by rejecting MTU values above U16MAX.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
Reject MTU values above U16_MAX (65535) in both TIPC_NL_MEDIA_SET and TIPC_NL_BEARER_SET validation paths, including tipc_udp_mtu_bad() and __tipc_nl_bearer_set().
Event History
Frequently Asked Questions
Who can exploit this issue?
A local attacker with low privileges can trigger the flaw. The provided crash stack notes that it can be triggered by an unprivileged user through a user namespace.
What MTU values trigger the most severe behavior?
An MTU value greater than 65535 passes the affected validation and is truncated to a 16-bit value. Setting 65536 truncates to zero and can cause a division by zero, while values from 65537 through 131071 can produce small incorrect MTUs and link malfunctions.
Which configuration paths are affected?
Two independent TIPC netlink configuration paths are affected: MEDIA_SET through tipc_udp_mtu_bad(), and BEARER_SET through the validation in __tipc_nl_bearer_set(). Both accept user-supplied MTU values without enforcing the required upper bound.