{"id":"CVE-2026-99074","title":"ipv4: stop PMTU walk when nexthop group shrinks","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: stop PMTU walk when nexthop group shrinks\n\nCommit 7d3f3b4367f3 (\"net: ipv4: Cache pmtu for all packet paths if\nmultipath enabled\") made __ip_rt_update_pmtu() upda…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 3bed2abab4a682d426624ce9add9d7b6d475d4e4 < 7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a","Linux >= 7f5005457b3072fe1ddf15bfef869f2a1d98e05e < c60d17d6dd61adc761ac6f65a008fefbc54cbf87","Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < c6d670ac656badfd0e15355e07a13a6bdf3b69fd","Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < f27483f9975b5065ff67054cc7eb8edac6083488","Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < 6619e01855e65ef35723685a557e3eb106f4ecf5","Linux fc07a232326a623d0be482e307c08ea7049c2846","Linux b1f7bdee5750d6cbb9497140cd6582abc5fdcb9e","Linux >= 6.6.79 < 6.6.160","Linux >= 6.12.16 < 6.12.113","Linux >= 5.15.179 < 5.16","Linux >= 6.1.129 < 6.2","Linux 6.13"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:23:17.866Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-99074","references":[{"url":"https://git.kernel.org/stable/c/7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a"},{"url":"https://git.kernel.org/stable/c/c60d17d6dd61adc761ac6f65a008fefbc54cbf87"},{"url":"https://git.kernel.org/stable/c/c6d670ac656badfd0e15355e07a13a6bdf3b69fd"},{"url":"https://git.kernel.org/stable/c/f27483f9975b5065ff67054cc7eb8edac6083488"},{"url":"https://git.kernel.org/stable/c/6619e01855e65ef35723685a557e3eb106f4ecf5"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.513Z","slug":"CVE-2026-99074","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nipv4: stop PMTU walk when nexthop group shrinks\n\nCommit 7d3f3b4367f3 (\"net: ipv4: Cache pmtu for all packet paths if\nmultipath enabled\") made __ip_rt_update_pmtu() update every path.\n\nFor nexthop objects, fib_info_num_path() and fib_info_nhc()\nindependently load nh->nh_grp.  RCU protects each group's lifetime but\ndoes not make the loads observe the same group.  If replacement shrinks\nthe group after the loop accepts an index, fib_info_nhc() returns NULL\nand update_or_create_fnhe() dereferences it.\n\nA deterministic probe only widened the existing window between the real\noperations.  On v7.2, an RTM_NEWNEXTHOP replacement published a\none-member group after the PMTU reader accepted index 1 from a two-member\ngroup, producing:\n\n  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]\n  RIP: update_or_create_fnhe+0x45/0x15b0\n\nStop when the indexed path is absent.  Groups are dense, so no later\nindex exists in that snapshot.  The same real-writer window completed\n114,423 PMTU iterations without an oops with this check.  A reproducer\nis available on request.\n\nReplacement requires CAP_NET_ADMIN in the network namespace.  Where\nunprivileged user namespaces are permitted, a local user can obtain it\nin a new user and network namespace.\n\n## Affected\n\n- `Linux >= 3bed2abab4a682d426624ce9add9d7b6d475d4e4 < 7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a`\n- `Linux >= 7f5005457b3072fe1ddf15bfef869f2a1d98e05e < c60d17d6dd61adc761ac6f65a008fefbc54cbf87`\n- `Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < c6d670ac656badfd0e15355e07a13a6bdf3b69fd`\n- `Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < f27483f9975b5065ff67054cc7eb8edac6083488`\n- `Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < 6619e01855e65ef35723685a557e3eb106f4ecf5`\n- `Linux fc07a232326a623d0be482e307c08ea7049c2846`\n- `Linux b1f7bdee5750d6cbb9497140cd6582abc5fdcb9e`\n- `Linux >= 6.6.79 < 6.6.160`\n- `Linux >= 6.12.16 < 6.12.113`\n- `Linux >= 5.15.179 < 5.16`\n- `Linux >= 6.1.129 < 6.2`\n- `Linux 6.13`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}