{"id":"CVE-2026-98393","revision":"8cade432d40145a08307e3ed506ce4f7","records":[{"revision":"8cade432d40145a08307e3ed506ce4f7","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-98393","aliases":[],"title":"net: ipv4: Fix UDP length overflow with PMTU discover and big MTU","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv4: Fix UDP length overflow with PMTU discover and big MTU\n\nThis commit bounds cork->base.fragsize to IP_MAX_MTU to avoid a\npossible overflow of UDP length that triggers a WARN in\nudp_set_len_short when setsockopt IP_MTU_DISCOVER is set to\nIP_PMTUDISC_PROBE, and a large packet is sent over a netdev with an\nunusually large MTU.\n\nSteps to reproduce:\n\n1. Set device MTU bigger than IP_MAX_MTU + 20. cork->base.fragsize will\n   be set to that MTU in ip_setup_cork.\n2. Set IP_MTU_DISCOVER to IP_PMTUDISC_PROBE. It lets maxnonfragsize be\n   set to device MTU (cork->fragsize) in __ip_append_data, rather than\n   to IP_MAX_MTU.\n3. Send 65528 bytes of payload (+8 bytes of UDP header, +20 bytes of\n   IPv4 header). Device MTU allows it (it's only one byte bigger than\n   IP_MAX_MTU + IPv4 header, and the device MTU is bigger than that).\n4. The UDP length in the built packet is 65536, which overflows the\n   16-bit length field and triggers the WARN in udp_set_len_short.\n\nNote: IP_PMTUDISC_DO with IPv4 is safe, because ip_dst_mtu_maybe_forward\nalways clamps at IP_MAX_MTU, unlike ip6_dst_mtu_maybe_forward.\n\nThe Fixes tag points at the first commit where I could reproduce the\noverflow with IPv4 and IP_PMTUDISC_PROBE.","state":0,"publishedAt":"2026-10-14T13:25:56.697+00:00","modifiedAt":"2026-10-19T09:18:46.601+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"net/ipv4/ip_output.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"daba287b299ec7a2c61ae3a714920e90e8396ad5\",\n                            \"lessThan\": \"83fedc4741210f75be8ca5b487985a242bf6f18d\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"daba287b299ec7a2c61ae3a714920e90e8396ad5\",\n                            \"lessThan\": \"81f540827d243b8dad76c1f44e70ea31719f393c\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"daba287b299ec7a2c61ae3a714920e90e8396ad5\",\n                            \"lessThan\": \"b83641e0ab8b20eefcc4cdc5a059f897375291a2\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"net/ipv4/ip_output.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"3.13\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"3.13\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.53\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2.7\",\n                            \"lessThanOrEqual\": \"7.2.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.3\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/83fedc4741210f75be8ca5b487985a242bf6f18d","https://git.kernel.org/stable/c/81f540827d243b8dad76c1f44e70ea31719f393c","https://git.kernel.org/stable/c/b83641e0ab8b20eefcc4cdc5a059f897375291a2"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98393","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-98393","identifiers":["CVE-2026-98393"]},"retained":false,"historicalAffected":[]}],"coverage":[]}