{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-68297", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-68297" ], "published": "2026-08-10T12:08:00Z", "summary": "tipc: fix u16 MTU truncation in media and bearer MTU validation", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix u16 MTU truncation in media and bearer MTU validation\n\nBoth TIPC_NL_MEDIA_SET and TIPC_NL_BEARER_SET accept user-supplied\nMTU values but only enforce a minimum bound, not a maximum. When a user\nsets the MTU to a value exceeding U16_MAX (65535), it passes validation\nbut is silently truncated when assigned to u16 fields l->mtu and\nl->advertised_mtu in tipc_link_create(). Values like 65536 (0x10000)\ntruncate to 0, causing a division by zero in tipc_link_set_queue_limits()\nwhich computes TIPC_MAX_PUBL / (l->mtu / ITEM_SIZE). Other overflowing\nvalues (e.g. 65537-131071) produce small incorrect MTU values, resulting\nin link malfunction behaviors.\n\nCrash stack (triggered as unprivileged user via user namespace):\n\n tipc_link_set_queue_limits net/tipc/link.c:2531\n tipc_link_create net/tipc/link.c:520\n tipc_node_check_dest net/tipc/node.c:1279\n tipc_disc_rcv net/tipc/discover.c:252\n tipc_rcv net/tipc/node.c:2129\n tipc_udp_recv net/tipc/udp_media.c:392\n\nTwo independent paths lack the upper bound check:\n1. tipc_udp_mtu_bad() -- called from __tipc_nl_media_set() (MEDIA_SET)\n2. inline check in __tipc_nl_bearer_set() at bearer.c:1160 (BEARER_SET)\n\nFix both by rejecting MTU values above U16_MAX.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.183", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-68297" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/8bfdfe0dbb36a650b7c4dec1aeae078319938a0b" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/dc4b577a083b361d25e118dc96d8281255ebe22c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/dfdfd987f1917c84766e097a6120a1f3f1634940" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f02334a9e378f7e07232b26dc3d2ab353339f040" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f4013598b69457dbea350df52e52daea6faef8eb" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/1b8fb5a20508bfb0db854e01214888c761b3a911" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/c1cda72f6acec02ebd45d913bf8527ff77336ba6" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/9f29cd8a8e7901a2617c8064ce9f50fc67b97cb8" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-19T16:47:12Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The attack begins with a local TIPC netlink command (TIPC_NL_BEARER_SET/TIPC_NL_MEDIA_SET) setting an out-of-range MTU, with the crash/corruption then triggered by locally generated discovery traffic and sendmsg() in the attacker's own network namespace.\nAC:L - The attacker fully controls both the bad MTU value and the discovery packet that creates the link, so the truncation and subsequent divide-by-zero or undersized-fragment path trigger deterministically on every attempt.\nPR:L - Both netlink ops are gated by GENL_UNS_ADMIN_PERM, i.e. CAP_NET_ADMIN in the owning user namespace, which any unprivileged user obtains via `unshare -Urn`; the commit message explicitly reports the crash reproduced as an unprivileged user through a user namespace.\nUI:N - The attacker performs every step (bearer setup, MTU configuration, packet injection, sendmsg) with no action from any other user or administrator.\nS:U - The truncated MTU corrupts only kernel state within the same kernel security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - Truncated MTUs below the TIPC header size propagate into tipc_msg_build() as pktmax, driving negative fragment remainders and oversized copies into undersized skbs; the resulting heap corruption and adjacent-object exposure can be leveraged to read kernel memory.\nI:H - The undersized-fragment path writes INT_H_SIZE plus header bytes and then a negative-length (huge unsigned) user copy into a buffer allocated at the truncated MTU size, giving an attacker-controlled linear heap overflow suitable for control-flow hijacking.\nA:H - MTU values truncating to under 20 make tipc_link_set_queue_limits() divide by zero inside tipc_link_create(), which runs in softirq context from tipc_udp_recv()/tipc_disc_rcv(), producing a kernel oops that is typically fatal in interrupt context." } } }