fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT

Description

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

Scores

No CVSS score yet: neither the CNA, CISA nor NVD has scored this CVE. NVD status: Received.

EPSS (exploitation in 30 days)

0.22% · top 88% of all CVEs (11 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: Not scored.

Affected products

• Linux · Linux

  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < fd20220f86947d66d4dba2d76f13a28dbd86ef30
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < 46b1ffb7e169c7e401dd890b29e55dbc261f8f01
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < 7f4ba56f5d310dd018972916167985010a5d66a1
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < 8b43f40798bb2758489fbbcae7e841ad4443c213
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < b1229b210ef5a39c58be665e6798203751411842
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221
  • affected 23461551c00628c3f3fe9cf837bf53cf8f212b63 – < d22609f3d13fc5baacd92c222731b03c593401db

• Linux · Linux

  • affected 3.18
  • unaffected < 3.18
  • unaffected 5.10.271 – ≤ 5.10.*
  • unaffected 5.15.222 – ≤ 5.15.*
  • unaffected 6.1.189 – ≤ 6.1.*
  • unaffected 6.6.158 – ≤ 6.6.*
  • unaffected 6.12.112 – ≤ 6.12.*
  • unaffected 6.18.55 – ≤ 6.18.*
  • unaffected 7.2.9 – ≤ 7.2.*
  • unaffected 7.3 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-103586 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-98541](https://cveledger.app/badge/CVE-2026-98541.svg)](https://cveledger.app/cve/CVE-2026-98541)

Record last updated 19 Oct 2026, 09:21 UTC.