# CVE-2026-99055: tcp: reject net_iov in zerocopy receive mapping hints


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** BELL-CVE-2026-99055, DEBIAN-CVE-2026-99055, GHSA-7h6j-x293-w79r, UBUNTU-CVE-2026-99055

## What is CVE-2026-99055?

CVE-2026-99055 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

tcp: reject net_iov in zerocopy receive mapping hints

After copying a readable prefix, receive_fallback_to_copy() asks
tcp_zerocopy_set_hint_for_skb() where page mapping can resume. If the
next skb is unreadable, find_next_mappable_frag() passes its net_iov
fragment to can_map_frag().

skb_frag_page() returns NULL for a net_iov, but can_map_frag()
dereferences it in PageCompound(). A v7.2 KASAN run on a connected TCP
socket with 64 readable bytes followed by a 4096-byte NET_IOV_DMABUF
fragment reported:

  BUG: KASAN: null-ptr-deref in can_map_frag
  tcp_zerocopy_receive -> can_map_frag
  Kernel panic - not syncing: KASAN: panic_on_warn set

The diagnostic inserted the net_iov directly because the test host has
no devmem-capable NIC. Hardware end-to-end reachability remains untested
and requires CONFIG_NET_DEVMEM plus a supported DMA-buf-bound RX queue.

Reject all net_iov fragments before skb_frag_page(). This covers both
DMABUF and IOURING net_iov types while leaving page-backed checks
unchanged. With the guard, the same queue copied the readable prefix,
returned a 4096-byte skip hint, and completed without a fault.

## Which versions are affected by CVE-2026-99055?


## How do I fix CVE-2026-99055?

Upgrade to a fixed version.

## Is CVE-2026-99055 being exploited?

There is no known exploitation of CVE-2026-99055 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99055 and fix it if it is affected.

What it is: CVE-2026-99055 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99055 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-2026-99055/ (Markdown: https://insights.sbomify.com/CVE-2026-99055/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99055
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99055
- OSV: https://osv.dev/vulnerability/CVE-2026-99055

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99055/
Summaries are generated and may contain mistakes; the official description above is the record.