# CVE-2026-98432: ipv4: free inet_opt and ireq_opt after an RCU grace period

> A use-after-free vulnerability in the Linux kernel IPv4 stack allows remote attackers to cause a denial of service or potentially execute code via crafted TCP packets.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** AZL-108246, BELL-CVE-2026-98432, DEBIAN-CVE-2026-98432, GHSA-qp6h-4hvh-qqqc, UBUNTU-CVE-2026-98432

## What is CVE-2026-98432?

CVE-2026-98432 is a critical use after free vulnerability in Linux, published on 15 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ipv4: free inet_opt and ireq_opt after an RCU grace period

tcp_v4_syn_recv_sock() transfers ownership of ireq->ireq_opt to the
child socket (newinet->inet_opt) without copying it.

Another cpu can concurrently process a retransmitted SYN for the same
request socket, and send a SYNACK from tcp_check_req().
tcp_v4_send_synack() and inet_csk_route_req() read ireq->ireq_opt
under rcu_read_lock() only, and ip_build_and_send_pkt() and
ip_options_build() then read opt->optlen twice.

Note that the SYNACK timer itself is not an issue: it holds a
reference on its request socket, and inet_csk_reqsk_queue_drop()
calls timer_delete_sync() before the child can be freed.

Since commit 079096f103fa ("tcp/dccp: install syn_recv requests
into ehash table"), request sockets are processed without holding
the listener lock, so nothing prevents the child socket from being
freed while the SYNACK is still being built. TCP child sockets do
not have SOCK_RCU_FREE, and inet_sock_destruct() frees inet_opt
with a plain kfree(), leading to a use-after-free in
ip_options_build().

A similar issue exists with request socket migration
(net.ipv4.tcp_migrate_req=1, or a BPF_SK_REUSEPORT_SELECT_OR_MIGRATE
program). reqsk_timer_handler() clones the request socket with
inet_reqsk_clone(), so that the old request socket and its clone
share the same ireq_opt, then reqsk_migrate_reset() clears the
pointer in the old one. Another cpu holding a reference on the old
request socket can still be using these options (sending a SYNACK,
or creating a child in tcp_v4_syn_recv_sock()) when the clone is
freed, and tcp_v4_reqsk_destructor() also uses a plain kfree().

Readers already use RCU, and other paths replacing inet_opt
(do_ip_setsockopt(), cipso_v4_sock_setattr()...) already use
kfree_rcu(). Use kfree_rcu() in inet_sock_destruct() and
tcp_v4_reqsk_destructor() as well.

IPv6 is not affected by the first issue, because tcp_v6_syn_recv_sock()
duplicates the options. tcp_v6_reqsk_destructor() has the same
migration issue with ipv6_opt, which is only set by CALIPSO. This
will be addressed in a separate patch.

## Which versions are affected by CVE-2026-98432?


## How do I fix CVE-2026-98432?

Apply the vendor's patch.

## Is CVE-2026-98432 being exploited?

There is no known exploitation of CVE-2026-98432 in the wild and no public exploit code.

Public exploit code:

- Race trigger, heap-reuse oracle, pcap analysis, detection and mitigation tooling for CVE-2026-98432 (Linux IPv4/TCP ireq_opt use-after-free). (github_poc): https://github.com/H1z3-br0/CVE-2026-98432
- cve-2026-98432 audit script (ipv4 TCP inet_opt/ireq_opt use-after-free) (github_poc): https://github.com/Quaerendir/cve-2026-98432-audit
- https://github.com/suominen/CVE-2026-98432 (github_poc): https://github.com/suominen/CVE-2026-98432
- kpatch livepatch for CVE-2026-98432 (and CVE-2026-99999) on AlmaLinux and Rocky Linux 8, 9 and 10 (github_poc): https://github.com/nsrg-fmlorg/kpatch-cve-2026-98432
- Temporary mitigation for CVE-2026-98432 (Linux IPv4 TCP ireq_opt use-after-free): drop IPv4 TCP with IP options, disable MPTCP. Tested scripts + verification. EN/KO. (github_poc): https://github.com/typhoon1217/cve-2026-98432-mitigation
- Linux kernel IPv4 SYN IP-options use-after-free CVE-2026-98432 Mitigation work (Ansible Role) (github_poc): https://github.com/axisops/CVE-2026-98432

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98432 and fix it if it is affected.

What it is: CVE-2026-98432 is a critical use after free vulnerability in Linux, published on 15 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98432 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98432/ (Markdown: https://insights.sbomify.com/CVE-2026-98432/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98432
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98432
- OSV: https://osv.dev/vulnerability/CVE-2026-98432

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98432/
Summaries are generated and may contain mistakes; the official description above is the record.