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CVE-2026-98541

fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.112, and 2 more
None on Exploit-DB, Metasploit or GitHub

Summary

In the Linux kernel, the following vulnerability has been resolved: fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT Commit 7a9bc9e3f423 ("fou: Don't allow 0 for FOU_ATTR_IPPROTO.") added NLA_POLICY_MIN(NLA_U8, 1) to fou_nl_policy[FOU_ATTR_IPPROTO], which rejects an explicitly supplied FOU_ATTR_IPPROTO == 0 attribute with -ERANGE. However, FOU_ATTR_IPPROTO is an optional netlink attribute. When a user sends FOU_CMD_ADD with FOU_ATTR_TYPE set to FOU_ENCAP_DIRECT and omits FOU_ATTR_IPPROTO entirely, nla_policy validation succeeds and parse_nl_config() leaves cfg->protocol as 0 (from memset(cfg, 0, sizeof(*cfg))). fou_create() then creates a FOU_ENCAP_DIRECT socket with fou->protocol == 0. In fou_udp_recv(), returning -fou->protocol to udp_queue_rcv_one_skb() triggers IP protocol resubmission when fou->protocol > 0, whereas returning 0 tells the UDP tunnel layer that the skb was consumed without freeing it. When fou->protocol == 0, every packet received on the socket returns 0 from fou_udp_recv() and leaks the sk_buff. Reject FOU_ENCAP_DIRECT when !cfg->protocol in fou_create() so that creating a direct encapsulation port without FOU_ATTR_IPPROTO fails with -EINVAL while leaving FOU_CMD_DEL and FOU_CMD_GET (which share parse_nl_config()) unaffected. Tested in QEMU against Linux 7.3.0-rc3 by sending a FOU_CMD_ADD Generic Netlink request with FOU_ATTR_PORT = 5555 and FOU_ATTR_TYPE = FOU_ENCAP_DIRECT while omitting FOU_ATTR_IPPROTO. On the unfixed kernel, FOU_CMD_ADD succeeds (err = 0), FOU_CMD_GET reports fou->type = 1 and fou->protocol = 0, and sending 4000 UDP packets to 127.0.0.1:5555 leaks all 4000 sk_buffs (SUnreclaim in /proc/meminfo grows from 41456 kB to 59008 kB, +17552 kB); with this patch applied, FOU_CMD_ADD is rejected with -EINVAL (-22).

Timeline

  1. CVE published
  2. Record last updated

Affected versions

  • Linux Linux

    From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in fd20220f86947d66d4dba2d76f13a28dbd86ef30; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in 46b1ffb7e169c7e401dd890b29e55dbc261f8f01; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in 7f4ba56f5d310dd018972916167985010a5d66a1; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in 8b43f40798bb2758489fbbcae7e841ad4443c213; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in b1229b210ef5a39c58be665e6798203751411842; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221; From 23461551c00628c3f3fe9cf837bf53cf8f212b63 · fixed in d22609f3d13fc5baacd92c222731b03c593401db

  • Linux Linux

    3.18

  • KernelLinux

    From 3.18.0 · fixed in 5.10.271; From 5.11.0 · fixed in 5.15.222; From 5.16.0 · fixed in 6.1.189; From 6.2.0 · fixed in 6.6.158; From 6.7.0 · fixed in 6.12.112; From 6.13.0 · fixed in 6.18.55; From 6.19.0 · fixed in 7.2.9

References 8

git.kernel.org