---
id: "CVE-2026-99055"
kind: "vulnerability"
aliases: ["CVE-2026-99055"]
title: "Linux kernel: TCP zerocopy receive can crash on device-memory fragments"
severity: "unknown"
cvss: null
epss: 0.00209
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "kernel", "linux", "network-stack", "self-hosted", "tcp"]
not_affected_if: ["default-config"]
published_at: "2026-10-23T13:17:29+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99055", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-99055", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux kernel: TCP zerocopy receive can crash on device-memory fragments

In the Linux kernel's TCP zerocopy receive path, a socket that reads a readable prefix followed by an unreadable device-memory (net_iov) fragment dereferences a null page pointer, causing a kernel crash. The sources describe a denial of service (kernel panic) observed under KASAN; they do not describe code execution.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check whether the kernel is built with `CONFIG_NET_DEVMEM` enabled, for example `grep CONFIG_NET_DEVMEM /boot/config-$(uname -r)`
- Check the running kernel version with `uname -r` and compare it to the fixed release in the kernel stable tree (unknown from the sources)
- Check whether the host uses devmem TCP or DMA-buf bound RX queues, which the sources say are required for reachability

## Fix

- Update the Linux kernel to a stable release that includes the commit 'tcp: reject net_iov in zerocopy receive mapping hints' (fixed version unknown from the sources)
- Hosts without `CONFIG_NET_DEVMEM` or without DMA-buf bound RX queues are not affected by the sources' description

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99055
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-99055

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_