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

Status: published. Published: 2026-07-25. Updated: 2026-11-10.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < f0d88a4cd03affff6c08adf6c63964e235aede43 (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < 27ddf4486c7dbf5bdd393fa8bef6b67179796d98 (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < 782708ca1ea1f68b8cbb5ea3a7f5f18d0000efae (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < e81f805824a8109504fce090641b17d135b48cd1 (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < 99206ce2244f8a3ed64298d0667c9055845a5dc7 (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < bbae351c0f32f7c200249e4aa6561b2b419dcf69 (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < a094ac95d3b69adfa1676eb9c8eae6835d4f1671 (affected, git); ≥ 91cc17c0e5e5ada156a8d5787a2509d263ea6bbf; < efb8763d7bbb40cff4cc55a6b62c3095a038149c (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.24 (affected); ≥ 0; < 2.6.24 (unaffected, semver); ≥ 5.10.261; ≤ 5.10.* (unaffected, semver); ≥ 5.15.212; ≤ 5.15.* (unaffected, semver); ≥ 6.1.178; ≤ 6.1.* (unaffected, semver); ≥ 6.6.145; ≤ 6.6.* (unaffected, semver); ≥ 6.12.96; ≤ 6.12.* (unaffected, semver); ≥ 6.18.39; ≤ 6.18.* (unaffected, semver); ≥ 7.1.4; ≤ 7.1.* (unaffected, semver); ≥ 7.2; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CVSS 3.1: 7.1 (high); CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H; source: CNA: Linux

- CISA KEV: No listing in collected sources

- EPSS: 0.14% as of 2026-11-09; percentile 3.24%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-190

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/f0d88a4cd03affff6c08adf6c63964e235aede43 (CNA: Linux)

- https://git.kernel.org/stable/c/27ddf4486c7dbf5bdd393fa8bef6b67179796d98 (CNA: Linux)

- https://git.kernel.org/stable/c/782708ca1ea1f68b8cbb5ea3a7f5f18d0000efae (CNA: Linux)

- https://git.kernel.org/stable/c/e81f805824a8109504fce090641b17d135b48cd1 (CNA: Linux)

- https://git.kernel.org/stable/c/99206ce2244f8a3ed64298d0667c9055845a5dc7 (CNA: Linux)

- https://git.kernel.org/stable/c/bbae351c0f32f7c200249e4aa6561b2b419dcf69 (CNA: Linux)

- https://git.kernel.org/stable/c/a094ac95d3b69adfa1676eb9c8eae6835d4f1671 (CNA: Linux)

- https://git.kernel.org/stable/c/efb8763d7bbb40cff4cc55a6b62c3095a038149c (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-64422; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-64422; retrieved 2026-11-10; source updated Not reported

Revision: 6abf6a69376ee8fa91ec439b09e5c812ef6a8488af0c7344bccf24f3cb897d5a

Canonical: https://y2.dev/cve/CVE-2026-64422

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