CVE-2026-64422 in Linux
Summary
by MITRE • 07/25/2026
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.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability resides in the linux kernel's ipv4 networking stack, specifically affecting tcp reordering sysctl handling and mtu probing mechanisms. The issue stems from improper validation of the net.ipv4.tcp_reordering parameter which is stored as an int type but subsequently copied into a u32 field within tcp socket structures. This type mismatch creates a potential security risk when negative values are written to the sysctl, as they wrap around to produce unexpectedly large unsigned values that can corrupt system behavior.
The flaw becomes particularly dangerous when combined with tcp_mtu_probing=2 configuration, where the wrapped reordering values can cause integer overflow during mtu probe size calculations. This overflow leads to out-of-bounds memory reads within the tcp_mtu_probe() function, potentially allowing attackers to access unauthorized memory regions or extract sensitive information from kernel space. The vulnerability represents a classic case of signed integer overflow leading to memory safety issues, which aligns with CWE-190 - Integer Overflow or Wraparound and CWE-129 - Improper Validation of Array Index.
The operational impact extends beyond simple information disclosure as this vulnerability could enable privilege escalation or denial of service conditions. Attackers could manipulate the tcp_reordering parameter to force the kernel into executing unintended code paths through memory corruption, potentially compromising system integrity. The issue affects all linux systems running kernel versions with the vulnerable tcp implementation and poses significant risk in environments where network services are exposed to untrusted clients.
The fix implements multiple defensive measures to address this vulnerability. First, the sysctl registration process now routes tcp_reordering writes through proc_dointvec_minmax() which enforces minimum values of 1 for both tcp_reordering and tcp_max_reordering parameters. This prevents negative or zero values from being accepted, eliminating the wraparound condition that leads to large unsigned values. Additionally, when registering network namespace tables, the implementation properly relocates extra2 pointers that reference init_net.ipv4 to ensure namespace-specific bounds are maintained, preventing cross-namespace parameter pollution.
The kernel code itself receives a hardening fix by computing size_needed as u64 instead of signed integer types within tcp_mtu_probe(). This prevents the bypassing of send queue and window checks that could occur through signed integer overflow, effectively closing the memory access vulnerability. These mitigations align with ATT&CK technique T1068 - Exploitation for Privilege Escalation and address the core issue identified in CVE-2023-XXXX where improper input validation leads to kernel memory corruption.
The solution demonstrates proper defensive programming practices by implementing input validation at multiple levels, ensuring type safety between different kernel subsystems, and applying appropriate bounds checking to prevent integer overflow conditions. These changes maintain backward compatibility while eliminating the security risk through proactive parameter validation and memory access protection mechanisms that align with modern kernel security hardening standards.