{"id":"CVE-2026-31503","summary":"udp: Fix wildcard bind conflict check when using hash2","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nudp: Fix wildcard bind conflict check when using hash2\n\nWhen binding a udp_sock to a local address and port, UDP uses\ntwo hashes (udptable-\u003ehash and udptable-\u003ehash2) for collision\ndetection. The current code switches to \"hash2\" when\nhslot-\u003ecount \u003e 10.\n\n\"hash2\" is keyed by local address and local port.\n\"hash\" is keyed by local port only.\n\nThe issue can be shown in the following bind sequence (pseudo code):\n\nbind(fd1,  \"[fd00::1]:8888\")\nbind(fd2,  \"[fd00::2]:8888\")\nbind(fd3,  \"[fd00::3]:8888\")\nbind(fd4,  \"[fd00::4]:8888\")\nbind(fd5,  \"[fd00::5]:8888\")\nbind(fd6,  \"[fd00::6]:8888\")\nbind(fd7,  \"[fd00::7]:8888\")\nbind(fd8,  \"[fd00::8]:8888\")\nbind(fd9,  \"[fd00::9]:8888\")\nbind(fd10, \"[fd00::10]:8888\")\n\n/* Correctly return -EADDRINUSE because \"hash\" is used\n * instead of \"hash2\". udp_lib_lport_inuse() detects the\n * conflict.\n */\nbind(fail_fd, \"[::]:8888\")\n\n/* After one more socket is bound to \"[fd00::11]:8888\",\n * hslot-\u003ecount exceeds 10 and \"hash2\" is used instead.\n */\nbind(fd11, \"[fd00::11]:8888\")\nbind(fail_fd, \"[::]:8888\")      /* succeeds unexpectedly */\n\nThe same issue applies to the IPv4 wildcard address \"0.0.0.0\"\nand the IPv4-mapped wildcard address \"::ffff:0.0.0.0\". For\nexample, if there are existing sockets bound to\n\"192.168.1.[1-11]:8888\", then binding \"0.0.0.0:8888\" or\n\"[::ffff:0.0.0.0]:8888\" can also miss the conflict when\nhslot-\u003ecount \u003e 10.\n\nTCP inet_csk_get_port() already has the correct check in\ninet_use_bhash2_on_bind(). Rename it to\ninet_use_hash2_on_bind() and move it to inet_hashtables.h\nso udp.c can reuse it in this fix.","modified":"2026-06-18T03:56:18.670126197Z","published":"2026-04-22T13:54:23.221Z","related":["SUSE-SU-2026:21841-1","SUSE-SU-2026:21845-1","SUSE-SU-2026:21860-1","openSUSE-SU-2026:20826-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31503.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0a360f7f73a06ac88f18917055fbcc79694252d7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/18d84c45def3671d5c89fbdd5d4ab8a3217fe4b4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2297e38114316b26ae02f2d205c49b5511c5ed55"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d6ace0dbcbb7fd285738bb87b42b71b01858c952"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e537dd15d0d4ad989d56a1021290f0c674dd8b28"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f1bed05a832ae79be5f7a105da56810eaa59a5f1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31503.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31503"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"30fff9231fad757c061285e347b33c5149c2c2e4"},{"fixed":"d6ace0dbcbb7fd285738bb87b42b71b01858c952"},{"fixed":"2297e38114316b26ae02f2d205c49b5511c5ed55"},{"fixed":"f1bed05a832ae79be5f7a105da56810eaa59a5f1"},{"fixed":"18d84c45def3671d5c89fbdd5d4ab8a3217fe4b4"},{"fixed":"0a360f7f73a06ac88f18917055fbcc79694252d7"},{"fixed":"e537dd15d0d4ad989d56a1021290f0c674dd8b28"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31503.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.33"},{"fixed":"6.1.168"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.131"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.80"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.21"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.11"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31503.json"}}],"schema_version":"1.7.5"}