CVE-2026-64414 Overview
CVE-2026-64414 is a Linux kernel vulnerability in the netfilter subsystem. The flaw affects how netfilter modules handle socket buffers (skb) containing unreadable fragments, such as those produced by devmem TCP where skb_frags_readable(skb) returns false. When the u32 classifier or related netfilter components process these buffers, skb_copy_bits() returns a negative error code that the affected code paths do not handle correctly.
The upstream fix updates xt_u32, gather_frags, nfnetlink_queue, and nfnetlink_log to safely bail out or restrict processing to the linear portion of the packet.
Critical Impact
A remote attacker can trigger a kernel-level denial of service by sending network traffic that causes affected netfilter modules to mishandle skbs with unreadable fragments.
Affected Products
- Linux kernel netfilter subsystem (xt_u32 module)
- Linux kernel nfnetlink_queue module
- Linux kernel nfnetlink_log module
Discovery Timeline
- 2026-07-25 - CVE-2026-64414 published to NVD
- 2026-07-27 - Last updated in NVD database
Technical Details for CVE-2026-64414
Vulnerability Analysis
The vulnerability affects multiple netfilter components that process socket buffers containing unreadable fragments. Devmem TCP introduced skbs whose fragment memory is not directly accessible via CPU loads, and skb_frags_readable(skb) reports these buffers as unreadable. When such skbs reach netfilter modules that were written before this constraint existed, calls to skb_copy_bits() fail and return a negative error code.
The xt_u32 iptables match module previously did not check this return value correctly, allowing execution to continue on failed copies. The nfnetlink_queue and nfnetlink_log modules attempted to copy entire packet contents including unreadable fragments, and the skb_zerocopy helpers did not propagate the readable flag. This caused inconsistent state and reachable error paths inside the kernel.
Root Cause
The root cause is missing input validation and improper handling of a new skb state introduced by devmem TCP. Netfilter code assumed all skb fragments were readable and did not verify the result of skb_copy_bits() before continuing. This is a kernel input validation flaw in packet fragment handling.
Attack Vector
Exploitation is network-based and requires no authentication or user interaction. An attacker sends crafted network traffic to a host that uses devmem TCP or otherwise produces skbs with unreadable fragments, and where netfilter rules exercise the xt_u32 match or logging via nfnetlink_queue or nfnetlink_log. The affected code paths can be triggered to cause a kernel-side availability impact.
No verified public exploit code is available for CVE-2026-64414. Technical details are described in the upstream kernel commits linked in the Linux stable tree.
Detection Methods for CVE-2026-64414
Indicators of Compromise
- Unexpected kernel warnings or oops messages referencing skb_copy_bits, xt_u32, nfnetlink_queue, or nfnetlink_log in dmesg output.
- Sudden loss of network processing or netfilter rule evaluation on hosts using devmem TCP.
- Elevated rates of dropped packets on interfaces attached to devmem TCP-enabled workloads.
Detection Strategies
- Monitor kernel logs for stack traces originating in netfilter fragment-handling functions.
- Audit iptables and nftables rule sets for use of the u32 match on hosts that participate in devmem TCP transfers.
- Track kernel version and patch level against the fixed commits listed in the upstream Linux stable tree.
Monitoring Recommendations
- Enable centralized syslog collection of dmesg and kernel ring buffer content across Linux fleets.
- Alert on repeated WARN_ON or BUG events tied to netfilter symbols.
- Correlate host crash or reboot events with traffic patterns from devmem TCP peers.
How to Mitigate CVE-2026-64414
Immediate Actions Required
- Identify Linux hosts running kernels that predate the fix commits 3b13e763, 57056be3, da5b5847, and fc5bfe63.
- Prioritize patching hosts that use devmem TCP or expose xt_u32, nfnetlink_queue, or nfnetlink_log on network-reachable paths.
- Restrict untrusted network access to affected systems until patched.
Patch Information
Upstream fixes are available in the Linux stable tree. Apply the patched kernel version distributed by your Linux vendor, or rebuild from the following commits: 3b13e763, 57056be3, da5b5847, and fc5bfe63.
Workarounds
- Remove or avoid iptables rules that use the u32 match module on hosts handling devmem TCP traffic.
- Disable nfnetlink_queue and nfnetlink_log targets on affected hosts if operationally feasible.
- Disable devmem TCP where not required by workloads.
# Verify whether the xt_u32 module is loaded
lsmod | grep -E 'xt_u32|nfnetlink_queue|nfnetlink_log'
# Unload the u32 match module if not required
sudo modprobe -r xt_u32
# Confirm running kernel version against vendor advisory
uname -r
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
