{"id":"CVE-2026-53070","summary":"sctp: disable BH before calling udp_tunnel_xmit_skb()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nsctp: disable BH before calling udp_tunnel_xmit_skb()\n\nudp_tunnel_xmit_skb() / udp_tunnel6_xmit_skb() are expected to run with\nBH disabled.  After commit 6f1a9140ecda (\"add xmit recursion limit to\ntunnel xmit functions\"), on the path:\n\n  udp(6)_tunnel_xmit_skb() -\u003e ip(6)tunnel_xmit()\n\ndev_xmit_recursion_inc()/dec() must stay balanced on the same CPU.\n\nWithout local_bh_disable(), the context may move between CPUs, which can\nbreak the inc/dec pairing. This may lead to incorrect recursion level\ndetection and cause packets to be dropped in ip(6)_tunnel_xmit() or\n__dev_queue_xmit().\n\nFix it by disabling BH around both IPv4 and IPv6 SCTP UDP xmit paths.\n\nIn my testing, after enabling the SCTP over UDP:\n\n  # ip net exec ha sysctl -w net.sctp.udp_port=9899\n  # ip net exec ha sysctl -w net.sctp.encap_port=9899\n  # ip net exec hb sysctl -w net.sctp.udp_port=9899\n  # ip net exec hb sysctl -w net.sctp.encap_port=9899\n\n  # ip net exec ha iperf3 -s\n\n- without this patch:\n\n  # ip net exec hb iperf3 -c 192.168.0.1 --sctp\n  [  5]   0.00-10.00  sec  37.2 MBytes  31.2 Mbits/sec  sender\n  [  5]   0.00-10.00  sec  37.1 MBytes  31.1 Mbits/sec  receiver\n\n- with this patch:\n\n  # ip net exec hb iperf3 -c 192.168.0.1 --sctp\n  [  5]   0.00-10.00  sec  3.14 GBytes  2.69 Gbits/sec  sender\n  [  5]   0.00-10.00  sec  3.14 GBytes  2.69 Gbits/sec  receiver","modified":"2026-07-16T03:31:05.311937745Z","published":"2026-06-24T16:30:11.816Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53070.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0de7db2eb27e82b983157016fa604b1ba664ae5f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2cd7e6971fc2787408ceef17906ea152791448cf"},{"type":"WEB","url":"https://git.kernel.org/stable/c/790093245e35040c2adb15f48970020425aa3f47"},{"type":"WEB","url":"https://git.kernel.org/stable/c/be3bfcb34bda04f6a350710db471d4133f950f2c"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53070.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-53070"},{"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":"046c052b475e7119b6a30e3483e2888fc606a2f8"},{"fixed":"be3bfcb34bda04f6a350710db471d4133f950f2c"},{"fixed":"0de7db2eb27e82b983157016fa604b1ba664ae5f"},{"fixed":"790093245e35040c2adb15f48970020425aa3f47"},{"fixed":"2cd7e6971fc2787408ceef17906ea152791448cf"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53070.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"6.12.95"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.37"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53070.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}