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CVE.org (no NVD analysis yet)· CNA Linux

CVE-2026-98541: fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT

Noroxi assessment

Priority: Monitor (action score 0/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.21% (FIRST EPSS).
  • Fixed version: Linux Linux 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6, 46b1ffb7e169c7e401dd890b29e55dbc261f8f01, 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221; azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 6.6.159.1-1.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6, 46b1ffb7e169c7e401dd890b29e55dbc261f8f01, 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221; azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 6.6.159.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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).

—No exploit Fix available
Published
Oct 18, 2026
Updated
Oct 19, 2026
EPSS
0.2% · 12th percentile
CWE
—

Report tools

JSON

Action score

0

Monitor

Low priority for now.

CVSS
0 / 40 · —
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 3.18affected
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before fd20220f86947d66d4dba2d76f13a28dbd86ef30affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before 46b1ffb7e169c7e401dd890b29e55dbc261f8f01affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before 7f4ba56f5d310dd018972916167985010a5d66a1affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before 8b43f40798bb2758489fbbcae7e841ad4443c213affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before b1229b210ef5a39c58be665e6798203751411842affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221affected · git
    • 23461551c00628c3f3fe9cf837bf53cf8f212b63 and later · before d22609f3d13fc5baacd92c222731b03c593401dbaffected · git
    • before 3.18not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.190-16.1.190-1
Debian:12linux-6.12before 6.12.113-1~deb12u16.12.113-1~deb12u1
Debian:13linuxbefore 6.12.113-16.12.113-1
Debian:14linuxbefore 7.2.9-17.2.9-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-98539Oct 18, 2026 · fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and murder syzbot's "WARNING in do_new_mount" saga
    0Monitor
  • ← EarlierCVE-2026-98540Oct 18, 2026 · fprobe: Terminate the fgraph_data list when the reservation is not filled
    0Monitor
  • Later →CVE-2026-98542Oct 18, 2026 · cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict
    0Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux3bcc1624cc1cdcc05b566475d6e848093ab2a8f6Vendor (CNA)
Linux Linux46b1ffb7e169c7e401dd890b29e55dbc261f8f01Vendor (CNA)
Linux Linux520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221Vendor (CNA)
Linux Linux7f4ba56f5d310dd018972916167985010a5d66a1Vendor (CNA)
Linux Linux8b43f40798bb2758489fbbcae7e841ad4443c213Vendor (CNA)
Linux Linuxb1229b210ef5a39c58be665e6798203751411842Vendor (CNA)
Linux Linuxd22609f3d13fc5baacd92c222731b03c593401dbVendor (CNA)
Linux Linuxfd20220f86947d66d4dba2d76f13a28dbd86ef30Vendor (CNA)
azl3 kernel 6.6.157.1-1 on Azure Linux 3.06.6.159.1-1 · Release NotesMicrosoft (MSRC)
debian:linux6.1.190-1 · Debian:12Package registry (OSV)
debian:linux-6.126.12.113-1~deb12u1 · Debian:12Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. Fix recordedsame day
  3. TodayNov 1, 2026+14 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

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No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

No CVSS vector for this record, so attack conditions can't be derived.

Weakness class (CWE)

—

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Exploit maturity— → none
  2. Fix✗ → ✓

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References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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