External risk intelligence

Linux Kernel NFSD SECINFO_NO_NAME Decode Error

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-53398

The vulnerability affects the Linux kernel NFSD (NFS server) component. While NFS is traditionally deployed in trusted, isolated internal networks or data centers and is rarely exposed directly to the public internet, it is a network service that can be reachable in some specific deployment architectures, making occasional internet exposure possible.

Halo Surface Signal: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A security flaw in the Linux kernel's network file system service could allow for a denial of service, impacting system stability and availability. This issue arises from an error in handling truncated data during security information decoding, which can lead to unexpected behavior.

A flaw exists in Linux kernel's network file system service.
Impacts system stability and availability of network file services.
Confirm relevance and exposure of Linux kernel network services.

Attack Path

How an attacker could exploit the issue

An attacker could target a Linux system by sending specially crafted network requests to the NFS server. This would involve interacting with the `NFSD` component, specifically when it processes `SECINFO_NO_NAME` requests. A failure during the decoding of these requests, due to a truncated data stream, could lead to a state where uninitialized data is used in subsequent operations, potentially allowing an attacker to compromise the system.

Network access to NFS server required.
Truncated RPC data triggers vulnerability.
Leads to denial of service or code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to trigger an error in the Linux kernel's NFS server (NFSD) when processing security information. If triggered, this error could lead to the reuse of uninitialized or stale data from previous operations, potentially impacting system stability and security.

System data integrity.
Malformed network requests.
Denial of service or data corruption.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the Linux kernel's NFSD component likely impacts teams managing Linux servers and the NFS service, such as infrastructure or platform teams. The first practical step is to identify all Linux systems running the NFS server, determine if these systems are externally facing or accessible from less trusted network segments, and confirm their business criticality. Understanding which teams are accountable for these servers and the NFS service will guide the remediation planning based on the identified risk.

Identify NFS server owners.
Verify external exposure and criticality.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Linux kernel NFSD component?

NFSD, or NFS Server, is a core part of the Linux kernel that enables a computer to share files and directories with other systems over a network. It implements the Network File System (NFS) protocol, allowing remote clients to mount these directories and interact with files as if they were stored locally. It is a fundamental service for distributed storage, cluster computing, and centralized file management in many Linux-based environments.

How does CVE-2026-53398 affect NFS operations?

This vulnerability is an Improper Initialization flaw occurring within the NFSD code that processes SECINFO_NO_NAME requests. When the server receives a truncated data stream, it may fail to properly clear or initialize specific data structures before they are reused. This leaves stale memory information in place, which the system then inadvertently processes, potentially leading to unstable behavior or errors in how the server handles security information for client requests.

Do I need to send specific data to trigger this vulnerability?

Yes, this bug is triggered by specially crafted network requests that cause the NFSD decoder to encounter a truncated data stream during a SECINFO_NO_NAME operation. Standard, well-formed NFS traffic will not trigger this issue. The vulnerability specifically relies on the decoder failing mid-operation, which causes the software to fall back on data left over from previous, unrelated memory operations.

How do I know if my systems are at risk for CVE-2026-53398?

According to Halo Surface Signal, risk depends on your deployment. While NFS is typically used in trusted, internal-only segments, any system reachable from the public internet or less-trusted network segments increases the potential for interaction. You should prioritize assessing Linux systems that run the NFS server service and are accessible beyond the immediate, secure data center perimeter.

What is the first step to address this Linux kernel issue?

Begin by inventorying your fleet to identify all systems running the NFS server service. Once identified, map these systems against your network architecture to confirm which are accessible from external or untrusted segments. Finally, coordinate with your infrastructure teams to prioritize these high-exposure systems for security updates as they become available from your Linux distribution vendors.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.