CVE-2025-38264: Linux nvme-tcp Vulnerability and Azure Linux Attestation

The Linux kernel vulnerability tracked as CVE-2025-38264 affects the NVMe-over-TCP host driver (nvme‑tcp) and was fixed upstream by defensive checks in the nvme TCP code; Microsoft’s public advisory names Azure Linux as a Microsoft product that “includes this open‑source library and is therefore potentially affected,” but that attestation is product‑scoped — it is an authoritative signal for Azure Linux only and does not by itself prove that no other Microsoft product could include the vulnerable code.

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Background / Overview​

The nvme‑tcp driver implements the NVMe over Fabrics (NVMe‑oF) TCP transport in the Linux kernel and appears as the module/driver nvme-tcp (CONFIG_NVME_TCP). The vulnerability CVE‑2025‑38264 was assigned after upstream kernel maintainers identified a request‑list handling flaw in the NVMe TCP code: nvme_tcp_handle_r2t did not validate that a request was not already part of a list, allowing a malformed or malicious R2T PDU to inject a loop into request list processing. The consequence is kernel memory corruption, repeated processing loops, or denial‑of‑service depending on how the out‑of‑bounds/list corruption is triggered. Multiple mainstream vulnerability trackers and distribution security pages have recorded the CVE and mapped it to kernel commits and fixed package releases; the upstream fixes were applied into the stable kernel series (commits referenced by the Linux kernel CVE announcement). Distributions have been shipping fixes on a rolling basis or listing which kernel packages contain the upstream correction. Why this matters operationally:

• The exploit vector mainly targets hosts that run NVMe‑oF services or that accept NVMe‑TCP PDUs from untrusted peers (for example, shared storage endpoints, multi‑tenant storage hosts).
• Impact is primarily availability (host oops/panic or corrupted kernel state), though higher‑impact outcomes can arise depending on where memory corruption lands.
• The flaw is in kernel code shipped by many Linux vendors; each downstream product must be validated per artifact and kernel configuration.

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What Microsoft actually said — and how to read it​

Microsoft’s Security Response Center entry for this CVE includes the sentence quoted by the user: that Azure Linux “includes this open‑source library and is therefore potentially affected,” and Microsoft added that they began publishing machine‑readable CSAF/VEX attestations in October 2025 and will update the CVE record if impact to additional products is identified. That wording is deliberate: it is a product‑level attestation — the company is stating which Microsoft product artifacts they have inventory‑checked and found to include the upstream component.
Important interpretive points:

• Attestation ≠ exclusivity. An attestation that Azure Linux is affected is authoritative for Azure Linux, but does not prove that other Microsoft products cannot contain the same upstream code. The absence of a separate attestation for another Microsoft product means it is not yet attested — effectively “unknown until verified,” not “proven safe.”
• Microsoft’s VEX/CSAF rollout began with Azure Linux as a pragmatic first product family; that’s why Azure Linux appears first in their published mappings. Microsoft explicitly said it will update the CVE (and the machine‑readable attestations) if additional Microsoft products are discovered to ship the component.

Two independent validations of the CVE and fix are available from public sources: the NVD entry for CVE‑2025‑38264 describes the vulnerability and the Linux kernel CVE announcement lists the exact commits that fix the issue. These independent sources corroborate the technical description and the fact the patch landed in the kernel stable trees.

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Technical details (concise)​

What is the faulty code path?​

• Location: drivers/nvme/host/tcp.c inside the Linux kernel.
• Function of interest: nvme_tcp_handle_r2t — responsible for handling R2T (Ready To Transfer) PDUs in NVMe‑TCP.
• Fault: The code failed to validate whether a request object being processed was already part of an existing list; a crafted R2T could cause the same request to be linked repeatedly or processed in a loop, leading to resource exhaustion, list corruption, or out‑of‑bounds memory activity.

Where the fix landed​

• Upstream maintainers applied small, targeted fixes in the stable kernel branches (the Linux kernel CVE announcement lists three stable commits that contain the remedy). Upgrading to a kernel release that includes those commits or applying vendor patches that incorporate those commits is the recommended remediation path.

Real‑world exploitability​

• Practical exploitation requires the ability to send malformed NVMe‑TCP PDUs to a host that processes NVMe‑TCP traffic — this typically limits exposure to hosts that run NVMe‑oF endpoints or accept TCP connections from untrusted networks.
• Many distributions and environments do not enable header digests or NVMe‑TCP endpoints by default; therefore exposure is artifact and configuration dependent.

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Is Azure Linux the only Microsoft product that includes the vulnerable library?​

Short, operational answer:

• No — Azure Linux is not necessarily the only Microsoft product that could include the vulnerable nvme‑tcp code. It is, however, the only Microsoft product Microsoft has publicly attested (via CSAF/VEX) as including the upstream component at the time of their advisory. That attestation is authoritative for Azure Linux and actionable for customers running those images; it is not a categorical guarantee that WSL, Marketplace images, or other Microsoft‑distributed kernel artifacts cannot carry the same components.

Why that nuance matters:

• Microsoft ships multiple Linux kernel artifacts and images across different product lines: the Azure Linux kernels (the first to be VEX‑mapped), the WSL2 kernel images Microsoft publishes, linux‑azure kernels used in some VM SKUs, curated Marketplace images, AKS node images, and other appliance or IoT images. Each artifact is a separately built kernel with its own configuration; whether the vulnerable code is present depends on:
  • The upstream kernel revision used,
  • Kernel configuration flags (e.g., whether NVME‑oF and CONFIG_NVME_TCP were enabled),
  • Whether an upstream fix was backported into that artifact's kernel tree.

Concrete examples of plausible Microsoft artifacts that may include the same kernel code:

• WSL2 (Windows Subsystem for Linux) — Microsoft maintains the WSL2 kernel source and distributes kernel images for WSL2; the WSL kernel config and version are publicly visible in the WSL2 repo and can be built with a different set of kernel options. That means some WSL kernel builds might include NVMe‑TCP support and could therefore be vulnerable if they predate the upstream patch and include the driver.
• linux‑azure / Marketplace / Azure node images — Some Azure VM images use Microsoft‑built kernels or kernels with selective backports. Those images should be validated by checking kernel version, vendor advisories, and Microsoft’s VEX outputs where available.

Operational takeaway: treat Microsoft’s public attestation for Azure Linux as a strong, machine‑readable signal for that product — and do not assume that other Microsoft‑supplied artifacts are automatically safe. Each artifact must be verified on its own merits.

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How to verify whether a Microsoft artifact you run is affected​

The following checklist is designed to be run artifact‑by‑artifact. It covers VMs, container hosts, WSL instances, offline images, and Marketplace/AKS node images.

On a running Linux host (VM, AKS node, container host)​

1. Identify the kernel release:
   • uname -r
2. Inspect kernel configuration for NVMe TCP:
   • If /proc/config.gz exists: zgrep -i NVME /proc/config.gz
   • Or inspect /boot/config-$(uname -r) and look for CONFIG_NVME_TCP, CONFIG_NVME, CONFIG_NVME_FABRICS.
3. Check whether the module is present/loaded:
   • lsmod | grep nvme
   • modinfo nvme-tcp (if modules are available under /lib/modules)
4. Search kernel logs for nvme_tcp errors or oops signatures:
   • journalctl -k | grep -i nvme
5. Compare kernel package changelogs with distro / vendor advisories for CVE references (e.g., Debian/Ubuntu/SUSE/Red Hat advisories) to confirm whether the vendor packaged the upstream commit. Many distros list the affected/fixed kernel versions for CVE‑2025‑38264.

For WSL2​

• Check WSL kernel version from inside WSL: uname -r.
• If using the default Microsoft‑supplied WSL kernel, confirm which WSL kernel release is installed and whether it contains nvme‑tcp or the upstream commit range; Microsoft publishes the WSL2 kernel source and configuration so operators can inspect the config before concluding safety. If using a custom WSL kernel (via %USERPROFILE%.wslconfig kernel=..., inspect that custom kernel’s configuration and modules.

For offline images or Marketplace VM images​

• Mount the image or extract the filesystem and inspect /boot and /lib/modules for kernel version and modules.
• Inspect any supplied SBOM or VEX/CSAF output for the image (Microsoft’s CSAF/VEX artifacts are being published and updated; the Azure Linux attestation is the first such dataset).
• Vendor‑provided Marketplace images should be validated against the publisher’s security advisories and the Azure Marketplace metadata.

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Remediation and mitigation guidance​

Primary remediation:

• Apply vendor patches / updated kernel packages that include the upstream fix and perform controlled reboots. The Linux kernel CVE team and distribution trackers point to specific stable commits that remediate the issue; vendors include those commits in updated kernel packages. Updating to a kernel version that contains the fixes is the recommended action. turn6search0

Short‑term mitigations (if immediate patching is impossible):

• Avoid accepting NVMe‑TCP connections from untrusted networks. Restrict access with firewall rules, VLANs, or administrative network segmentation.
• Disable or avoid negotiating header digests on NVMe stacks if your environment permits this (the exploit triggers in digest handling code paths in some variants). Note: disabling digests reduces protocol integrity protections; treat this as a temporary mitigation and understand the tradeoffs.
• Isolate and harden hosts that provide NVMe‑oF endpoints (use host firewalls, restrict management planes, and limit which tenants/networks can connect).
• Hunt for kernel oopses and configure crashdump (kdump) collection on critical hosts to capture evidence for post‑incident analysis.

Azure Linux customers:

• Follow Microsoft’s Azure Linux VEX/CSAF outputs and apply the Azure Linux kernel updates the vendor publishes for the attested kernel artifacts. Microsoft has committed to update its CVE/VEX entries if more products are found to be carriers.

WSL users:

• If the default WSL kernel is used, watch for Microsoft WSL updates distributed via Windows Update and the WSL2 kernel GitHub releases and apply them as needed. If a custom kernel is in use, build or obtain a kernel that includes the upstream fix and swap it in via .wslconfig then restart WSL (wsl --shutdown).

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Critical analysis — strengths, gaps, and risks​

Strengths and positive signals​

• Upstream fix was small and surgical. The Linux kernel community released targeted patches in the stable trees, making vendor backports and distribution updates practical and low risk for regressions.
• Distributions responded. Multiple distro trackers and vendor advisories (Debian, Ubuntu, Amazon Linux, Oracle Linux, etc. recorded the CVE and published fixes or mapped which kernel package versions contain the remedy. That reduces the friction for operators to patch.
• Microsoft’s VEX/CSAF transparency model is helpful. Publishing machine‑readable attestations for Azure Linux makes it easier for Azure customers to automate triage and remediation for the products explicitly attested. Microsoft’s commitment to update its VEX/CSAF outputs if additional products are discovered is a constructive operational practice.

Remaining gaps and risks​

• Attestations are phased, not exhaustive. Microsoft’s current VEX/CSAF coverage started with Azure Linux; the absence of attestations for other Microsoft artifacts is not proof they are unaffected. Org‑level automation that trusts a single vendor attestation as a global exclusion could leave blind spots.
• Artifact diversity increases verification workload. Microsoft distributes multiple kernel artifacts (WSL kernels, linux‑azure kernels, Marketplace images, AKS node images). Each must be verified by operators — either by trusting vendor attestations for that item or by performing artifact‑level checks (kernel config, modules present, package changelogs).
• Custom and partner images are a wild card. Marketplace appliances, partner images, or custom kernels derived from Microsoft or other vendor images may embed vulnerable code; these are often outside the scope of the vendor’s initial attestation work and can remain unverified for longer.

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Practical checklist for administrators (prioritized)​

1. Inventory: enumerate all Linux kernel images across the estate (Azure VMs, AKS node pools, Marketplace images, WSL2 instances, appliance/IoT images).
2. For each running artifact:
   • Run uname -r, inspect kernel config for CONFIG_NVME_TCP, check loaded modules (lsmod/modinfo), and inspect kernel logs for nvme signatures.
3. Cross‑reference vendor advisories (your distro vendor and Microsoft VEX/CSAF outputs) and upgrade kernels that do not include the fix.
4. Apply network mitigations for NVMe‑TCP endpoints until patched: firewall off untrusted access, isolate NVMe‑oF fabrics from public or tenant networks.
5. For WSL users: update WSL via Windows Update / WSL updates, or swap in a patched custom kernel via .wslconfig if necessary.
6. Monitor: centralize kernel logs, enable kdump on critical hosts, and hunt for nvme related oops/panic signatures.

A brief sample verification sequence for a running Linux VM:

1. uname -r
2. zgrep CONFIG_NVME_TCP /proc/config.gz
3. lsmod | grep nvme || modinfo nvme-tcp
4. journalctl -k | grep -Ei 'nvme|nvme_tcp|nvme-tcp'
5. Check distro package changelog for the kernel package for CVE references.

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Conclusion​

CVE‑2025‑38264 is a credible, upstream Linux kernel nvme‑tcp vulnerability that has been fixed by small upstream commits and tracked by multiple distribution security advisories. Microsoft’s public statement that Azure Linux includes the open‑source library and is therefore potentially affected is an authoritative attestation for the Azure Linux product family and an important signal for Azure customers to patch. However, that attestation is product‑scoped and does not prove that other Microsoft artifacts — notably the WSL2 kernel, linux‑azure kernels, Marketplace images, or custom/partner images — cannot include the vulnerable code. Each Microsoft‑distributed kernel artifact must be validated individually by checking kernel version, configuration, and vendor package changelogs, or by relying on Microsoft’s VEX/CSAF outputs if and when they are published for those artifacts. Operators should prioritize:

• patching attested Azure Linux images immediately;
• inventorying and validating other Microsoft kernel artifacts in their estate;
• applying network isolation/mitigations for NVMe‑TCP endpoints where patching cannot be immediate;
• integrating Microsoft’s CSAF/VEX feeds into automated triage pipelines and continuing artifact‑level verification for any un‑attested product.

The technical fixes are available upstream and in vendor advisories; the real work for defenders is systematic artifact verification and prioritized, coordinated patching across a heterogeneous estate.

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Source: MSRC Security Update Guide - Microsoft Security Response Center