CVE-2026-64422

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 namespaces 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.

Weakness

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• If possible, choose a language or compiler that performs automatic bounds checking.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
• Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
• Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
• Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
• Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
• Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
• Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/92.html

References

• https://git.kernel.org/stable/c/27ddf4486c7dbf5bdd393fa8bef6b67179796d98
• https://git.kernel.org/stable/c/782708ca1ea1f68b8cbb5ea3a7f5f18d0000efae
• https://git.kernel.org/stable/c/99206ce2244f8a3ed64298d0667c9055845a5dc7
• https://git.kernel.org/stable/c/a094ac95d3b69adfa1676eb9c8eae6835d4f1671
• https://git.kernel.org/stable/c/bbae351c0f32f7c200249e4aa6561b2b419dcf69
• https://git.kernel.org/stable/c/e81f805824a8109504fce090641b17d135b48cd1
• https://git.kernel.org/stable/c/efb8763d7bbb40cff4cc55a6b62c3095a038149c
• https://git.kernel.org/stable/c/f0d88a4cd03affff6c08adf6c63964e235aede43
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html