{"schema":"threatline.record/2","record":{"id":"CVE-2026-98393","aliases":[],"summary":"net: ipv4: Fix UDP length overflow with PMTU discover and big MTU","details":"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.","categories":["Operating systems"],"product":"Linux","vendor":"Linux","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98393","source_modified_at":"2026-10-19T09:18:46.601Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Linux","vendor":"Linux","versions":[{"version":"daba287b299ec7a2c61ae3a714920e90e8396ad5","lessThan":"83fedc4741210f75be8ca5b487985a242bf6f18d","status":"affected","versionType":"git"},{"version":"daba287b299ec7a2c61ae3a714920e90e8396ad5","lessThan":"81f540827d243b8dad76c1f44e70ea31719f393c","status":"affected","versionType":"git"},{"version":"daba287b299ec7a2c61ae3a714920e90e8396ad5","lessThan":"b83641e0ab8b20eefcc4cdc5a059f897375291a2","status":"affected","versionType":"git"}],"defaultStatus":"unaffected"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98393","source_modified_at":"2026-10-19T09:18:46.601Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Linux","vendor":"Linux","versions":[{"version":"3.13","status":"affected"},{"version":"0","lessThan":"3.13","status":"unaffected","versionType":"semver"},{"version":"6.18.53","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.7","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}],"defaultStatus":"affected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98393","source_modified_at":"2026-10-19T09:18:46.601Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"83fedc4741210f75be8ca5b487985a242bf6f18d","basis":"first unaffected version stated in the CVE record"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98393","source_modified_at":"2026-10-19T09:18:46.601Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"81f540827d243b8dad76c1f44e70ea31719f393c","basis":"first unaffected version stated in the CVE record"}],"cvss":null,"severity":null,"kev":{"listed":false},"epss":{"probability":0.00207,"percentile":0.10219,"score_date":"2026-10-23"},"published_at":"2026-10-14T13:25:56.697Z","modified_at":"2026-10-19T09:18:46.601Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-98393","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-19T09:18:46.601Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-98393","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://git.kernel.org/stable/c/83fedc4741210f75be8ca5b487985a242bf6f18d"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/81f540827d243b8dad76c1f44e70ea31719f393c"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/b83641e0ab8b20eefcc4cdc5a059f897375291a2"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"product","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-19T09:18:46.601Z","content_hash":"b29d4bf1b4a025d214d8df2e3fa8818b0876a005fda495ae778f3f8365f13fbb"}}