# CVE-2026-98374: tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()

> An unprivileged remote attacker can trigger a use-after-free in the Linux kernel TCP stack via crafted ICMP messages, potentially causing a crash or code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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:** 7 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** AZL-106734, BELL-CVE-2026-98374, DEBIAN-CVE-2026-98374, GHSA-2q84-vc4j-mp23, UBUNTU-CVE-2026-98374

## What is CVE-2026-98374?

CVE-2026-98374 is a high-severity use after free vulnerability in Linux, published on 7 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:

tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()

When tcp_send_synack() replaces the cloned SYN skb at the head of the
retransmit queue with a copy, it frees the original with
tcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack.
tp->retransmit_skb_hint keeps pointing at the freed
skbuff_fclone_cache object.

The dangling hint is read in tcp_verify_retransmit_hint() and used as
the root of the rbtree walk in tcp_xmit_retransmit_queue().  An
unprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with
an attacker-supplied ICMP fragmentation-needed message, after which a
simultaneous open frees the armed SYN skb:

  BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)
  Read of size 4 at addr ffff88800604d928 by task swapper/1/0
  Call Trace:
   tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)
   tcp_simple_retransmit (net/ipv4/tcp_input.c:3158)
   tcp_v4_err (net/ipv4/tcp_ipv4.c:587)

Sync the hint to the copy.

## Which versions are affected by CVE-2026-98374?


## How do I fix CVE-2026-98374?

Apply the vendor's patch.

## Is CVE-2026-98374 being exploited?

There is no known exploitation of CVE-2026-98374 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98374 and fix it if it is affected.

What it is: CVE-2026-98374 is a high-severity use after free vulnerability in Linux, published on 7 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-2026-98374 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-2026-98374/ (Markdown: https://insights.sbomify.com/CVE-2026-98374/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98374
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98374
- OSV: https://osv.dev/vulnerability/CVE-2026-98374

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98374/
Summaries are generated and may contain mistakes; the official description above is the record.