fou: Fix use-after-free in fou_create()

Answer in brief

CVE-2026-74496 records a High severity (CVSS 7.8) vulnerability in fou: Fix use-after-free in fou_create(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 15, 2026Updated Sep 21, 2026Source checked Sep 29, 2026First seen by HOL Aug 15, 2026Material review Sep 21, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.8
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=23461551c00628c3f3fe9cf837bf53cf8f212b63 <a28d8903bfe76089ea4bbdbff9976965f9ef8107 \|\| >=23461551c00628c3f3fe9cf837bf53cf8f212b63 <b14361aca6350ff7907b0e9903c7b94dc7d5d4a0	a28d8903bfe76089ea4bbdbff9976965f9ef8107, b14361aca6350ff7907b0e9903c7b94dc7d5d4a0
Linux/Linuxgeneric	3.18	Not reported
Linux/Linuxgeneric	>=23461551c00628c3f3fe9cf837bf53cf8f212b63 <58835985c035a8333742f829ad7e0889a082f9d3 \|\| >=23461551c00628c3f3fe9cf837bf53cf8f212b63 <9042867d4701728f0c6527215b11471759904d8f \|\| >=23461551c00628c3f3fe9cf837bf53cf8f212b63 <a28d8903bfe76089ea4bbdbff9976965f9ef8107 \|\| >=23461551c00628c3f3fe9cf837bf53cf8f212b63 <b14361aca6350ff7907b0e9903c7b94dc7d5d4a0	58835985c035a8333742f829ad7e0889a082f9d3, 9042867d4701728f0c6527215b11471759904d8f, a28d8903bfe76089ea4bbdbff9976965f9ef8107, b14361aca6350ff7907b0e9903c7b94dc7d5d4a0

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to a28d8903bfe76089ea4bbdbff9976965f9ef8107; Linux/Linux to 58835985c035a8333742f829ad7e0889a082f9d3 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 15, 2026

Sources and claim methodology

Upstream source description

In the Linux kernel, the following vulnerability has been resolved: fou: Fix use-after-free in fou_create() fou_create() publishes struct fou through sk_user_data before adding the new FOU port to the per-netns list. If fou_add_to_port_list() fails, the error path frees fou while it is still reachable through sk_user_data. A concurrent receive can then dereference the freed object in fou_from_sock(). This ordering issue was previously noted in the linked discussion. The failure is reachable when local port 0 is requested. Each socket binds to a different ephemeral port, but fou_cfg_cmp() compares the requested port 0 and reports -EALREADY once an entry already exists. Release the tunnel socket before freeing fou so sk_user_data is cleared first, and defer reclamation with kfree_rcu() to protect concurrent RCU readers. This matches the lifetime handling in fou_release().

Quoted source text, attributed separately from HOL analysis.