{"id":39064,"date":"2026-10-16T00:34:57","date_gmt":"2026-10-15T16:34:57","guid":{"rendered":"https:\/\/www.54iter.cn\/?vuln=cve-2026-98393"},"modified":"2026-10-16T00:34:57","modified_gmt":"2026-10-15T16:34:57","slug":"cve-2026-98393","status":"publish","type":"vuln","link":"https:\/\/www.54iter.cn\/?vuln=cve-2026-98393","title":{"rendered":"CVE-2026-98393 &#8211; In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv4: Fix UDP le"},"content":{"rendered":"<p>In the Linux kernel, the following vulnerability has been resolved:<\/p>\n<p>net: ipv4: Fix UDP length overflow with PMTU discover and big MTU<\/p>\n<p>This commit bounds cork-&gt;base.fragsize to IP_MAX_MTU to avoid a<br \/>\npossible overflow of UDP length that triggers a WARN in<br \/>\nudp_set_len_short when setsockopt IP_MTU_DISCOVER is set to<br \/>\nIP_PMTUDISC_PROBE, and a large packet is sent over a netdev with an<br \/>\nunusually large MTU.<\/p>\n<p>Steps to reproduce:<\/p>\n<p>1. Set device MTU bigger than IP_MAX_MTU + 20. cork-&gt;base.fragsize will<br \/>\n   be set to that MTU in ip_setup_cork.<br \/>\n2. Set IP_MTU_DISCOVER to IP_PMTUDISC_PROBE. It lets maxnonfragsize be<br \/>\n   set to device MTU (cork-&gt;fragsize) in __ip_append_data, rather than<br \/>\n   to IP_MAX_MTU.<br \/>\n3. Send 65528 bytes of payload (+8 bytes of UDP header, +20 bytes of<br \/>\n   IPv4 header). Device MTU allows it (it&#8217;s only one byte bigger than<br \/>\n   IP_MAX_MTU + IPv4 header, and the device MTU is bigger than that).<br \/>\n4. The UDP length in the built packet is 65536, which overflows the<br \/>\n   16-bit length field and triggers the WARN in udp_set_len_short.<\/p>\n<p>Note: IP_PMTUDISC_DO with IPv4 is safe, because ip_dst_mtu_maybe_forward<br \/>\nalways clamps at IP_MAX_MTU, unlike ip6_dst_mtu_maybe_forward.<\/p>\n<p>The Fixes tag points at the first commit where I could reproduce the<br \/>\noverflow with IPv4 and IP_PMTUDISC_PROBE.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In the Linux kernel, the following vulnerability has been resolved:<\/p>\n<p>net: ipv4: Fix UDP length overflow with PMTU discover and big MTU<\/p>\n<p>This commit bounds cork-&gt;base.fragsize to IP_MAX_MTU to avoid a<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-39064","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/39064","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=39064"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=39064"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=39064"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}