CVE-2026-72417 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: flowtable: Validate iph->ihl in nf_flow_ip4_tunnel_proto()
Add sanity check for iph->ihl field in nf_flow_ip4_tunnel_proto() before using it to compute the header size, avoiding out-of-bounds access with malformed IP headers. While at it, use iph->protocol instead of the hardcoded IPPROTO_IPIP constant when setting ctx->tun.proto and reference ctx->tun.hdr_size when updating ctx->offset.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability identified in the Linux kernel's netfilter subsystem represents a critical security flaw within the flowtable implementation that could enable attackers to execute arbitrary code or cause system crashes through malformed IP packet processing. This issue specifically affects the nf_flow_ip4_tunnel_proto() function which handles IPv4 tunnel protocol processing within the network flow table framework. The root cause stems from insufficient validation of the IP header's internet header length field, creating a potential out-of-bounds memory access condition that violates fundamental security principles of input validation and bounds checking.
The technical implementation flaw occurs when the kernel processes IPv4 tunnel packets without properly validating the iph->ihl field before using it to calculate header sizes. This field contains the Internet Header Length value in 32-bit words, and when malformed or maliciously crafted, it can cause the kernel to compute incorrect memory offsets leading to unauthorized memory access patterns. The vulnerability demonstrates a classic weakness in defensive programming where assumptions about input data integrity are not properly enforced before memory operations occur. According to CWE-129, this represents an implementation of insufficient input validation that allows for out-of-bounds reads and potential code execution. The flaw specifically impacts the kernel's network stack processing pipeline where tunnel packet headers are parsed and processed.
The operational impact of this vulnerability extends beyond simple denial-of-service scenarios to potentially enable remote code execution attacks against systems running vulnerable kernel versions. Network attackers could craft specially malformed IP packets with invalid header length values that would trigger the out-of-bounds access when processed by the netfilter subsystem. This creates a significant attack surface within enterprise networks where firewalls, routers, and network security appliances typically rely on kernel-level packet filtering capabilities. Systems utilizing the flowtable functionality for traffic management, load balancing, or security policy enforcement become particularly vulnerable as these components process large volumes of network traffic that could contain maliciously crafted packets.
The mitigation strategy involves implementing proper input validation before memory operations are performed, specifically checking the iph->ihl field against valid ranges before using it to compute header sizes. The fix requires adding bounds checking logic to ensure the header length field contains a legitimate value that would not cause overflow conditions when calculating memory offsets. Additionally, the patch addresses related issues by using the dynamic iph->protocol field instead of hardcoded constants, improving code maintainability and reducing potential errors in protocol handling. This approach aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as it prevents malicious actors from exploiting kernel vulnerabilities through crafted network traffic. The implementation also improves memory safety by ensuring proper header size calculations and offset management throughout the packet processing pipeline.
This vulnerability highlights the critical importance of robust input validation in kernel space operations where malformed data can lead to severe security consequences. The fix demonstrates proper defensive programming practices that should be applied across all kernel subsystems handling network packet processing, as these components are frequently targeted by attackers seeking to exploit memory corruption vulnerabilities. The resolution also emphasizes the need for continuous security auditing of kernel code paths that handle user-provided data, particularly in networking and security-related subsystems where the attack surface is extensive and the potential impact of exploitation is significant. Organizations should prioritize applying this patch immediately to protect against potential exploitation attempts targeting their network infrastructure components that rely on netfilter flowtable functionality.