# CVE-2026-98549: tcp: prevent collapsing skbs across boundary in rtx queue

> Attackers can cause cleartext transmission of encrypted data or connection stalls in Linux kernel TCP stacks using device offload features.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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:** 18 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** AZL-109181, BELL-CVE-2026-98549, DEBIAN-CVE-2026-98549, GHSA-p59j-fj4g-255h, UBUNTU-CVE-2026-98549

## What is CVE-2026-98549?

CVE-2026-98549 is a critical vulnerability in Linux, published on 18 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: prevent collapsing skbs across boundary in rtx queue

tcp_write_collapse_fence() sets TCP_SKB_CB(skb)->eor = 1 on
tcp_write_queue_tail(sk) to prevent skbs queued after a switch to
device encryption from being collapsed into earlier skbs.

The fence is a no-op if all earlier data has already been transmitted
when the switch happens: sk->sk_write_queue is empty. The not yet
acknowledged earlier skbs wait in sk->tcp_rtx_queue with eor 0.

On a subsequent retransmit or SACK shift, tcp_retrans_try_collapse() or
tcp_shift_skb_data() can then merge an skb queued after the switch into
one queued before it.

Both users of the fence are affected:

- psp: devices only encrypt skbs with skb->decrypted set. The merged skb
  keeps decrypted = 0 from the earlier skb, so merged data sent after
  psp_sock_assoc_set_tx() is retransmitted in cleartext.

- tls device offload: the merged skb straddles the start marker set in
  tls_set_device_offload(). The software fallback (fill_sg_in() returns
  -EINVAL) and the mlx5, nfp and funeth drivers cannot handle such an
  skb and drop it. Every retransmit rebuilds the same skb, so the
  connection stalls.

Fix this in two places, for defense in depth:

1. Fall back to tcp_rtx_queue_tail(sk) in tcp_write_collapse_fence()
   when tcp_write_queue_tail(sk) is NULL.

2. Check !skb_cmp_decrypted(to, from) in tcp_skb_can_collapse(), as
   tcp_skb_can_collapse_rx() does on receive. skb_shift(), which both
   collapse paths call, already has a DEBUG_NET_WARN_ON_ONCE() for this
   condition.

## Which versions are affected by CVE-2026-98549?


## How do I fix CVE-2026-98549?

Apply the vendor's patch.

## Is CVE-2026-98549 being exploited?

There is no known exploitation of CVE-2026-98549 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98549 and fix it if it is affected.

What it is: CVE-2026-98549 is a critical vulnerability in Linux, published on 18 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-2026-98549 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-2026-98549/ (Markdown: https://insights.sbomify.com/CVE-2026-98549/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98549
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98549
- OSV: https://osv.dev/vulnerability/CVE-2026-98549

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98549/
Summaries are generated and may contain mistakes; the official description above is the record.