CVE-2024-26881: Kernel patch fixes hns3 PTP null pointer crash in HiSilicon NICs

A small but important kernel fix — tracked as CVE-2024-26881 — plugs a null‑pointer crash in the Linux hns3 network driver that can be triggered when Precision Time Protocol (PTP/1588) packets arrive for HIP08-class HiSilicon devices. Microsoft’s published guidance for the CVE explicitly states that Azure Linux includes the implicated open‑source component and is therefore potentially affected, but that attestation is product‑scoped: it confirms inventory for Azure Linux, not an exhaustive statement that no other Microsoft product could include the same vulnerable code. Multiple upstream advisories, kernel mailing‑list postings, and distribution security notices document the bug, the upstream patch, and the practical impact — a kernel oops/panic when hardware timestamps are present but the driver’s PTP structures are not registered.

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Background / Overview​

The defect fixed by CVE‑2024‑26881 lives in the Linux kernel’s Hisilicon network subsystem driver family: hns3 (and the related hclge subcomponent used by some Hisilicon NICs). In certain HIP08-class devices the driver did not register a PTP (ptp) device structure, leaving a pointer (hdev->ptp) NULL. When the hardware nevertheless stamped an incoming packet (setting the RX timestamp valid bit, e.g., for 1588/PTP traffic), kernel code attempted to read hdev->ptp->flags and crashed with an immediate NULL‑pointer dereference. The crash trace printed by affected kernels shows the failure in functions such as hclge_ptp_get_rx_hwts and then bubbling through hns3 RX handling into a full kernel oops.
Why this matters operationally: a kernel oops or panic in the network receive path typically produces immediate host instability or denial of service. On multi‑tenant cloud hosts the outcome could be VM or node unavailability until a reboot or a patched kernel is installed. The fix for this CVE is straightforward at the code level (guarding accesses, ensuring ptp is registered before dereference), but operators still need to know whether their kernels actually include the implicated driver and whether the affected hardware exists in their environment. Distribution advisories and upstream commits confirm the fix; the canonical technical details and call traces are recorded in NVD and distribution security pages.

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The technical root cause, in plain language​

• The hardware (HIP08 NIC) can receive PTP/1588 frames and will mark the receive descriptor with a timestamp‑valid flag.
• The driver code assumed that if a timestamp flag was set it could safely dereference a ptp pointer in the device structure to read flags and timestamp information.
• On HIP08 devices the driver did not always register the ptp device object, so hdev->ptp could be NULL. The subsequent dereference produced a kernel NULL‑pointer dereference and crash.
• Upstream patches add a defensive check (and/or ensure the ptp device is registered when appropriate) so that the code either avoids the dereference or handles the absence of ptp gracefully.

This is a robustness/availability fix rather than a privilege‑escalation or remote arbitrary‑code execution flaw. The damage model is denial‑of‑service (kernel crash), not code injection. That said, on shared infrastructure a kernel panic can be as high‑impact as many other categories of vulnerability because it forces reboots and disrupts service. The published CVSS and distribution priorities reflect that operational weight.

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

Short answer: No — not necessarily. Microsoft’s public advisory language — that “Azure Linux includes this open‑source library and is therefore potentially affected” — is an authoritative, product‑scoped attestation for the Azure Linux distribution, and Microsoft has committed to updating CVE mappings if additional Microsoft products are identified as carriers. However, that wording should not be interpreted as a categorical statement that no other Microsoft product could include the same upstream driver. Whether another Microsoft product contains the vulnerable source depends on the exact kernel artifact, upstream commit range, and build configuration used to produce that artifact.
Why this nuance matters: Microsoft builds and ships many different Linux artifacts (Azure Linux images, kernels used in specialized appliances, kernel trees for WSL2, linux‑azure variants, AKS node images, partner‑distributed images). Each artifact is an independent kernel build that may enable or disable different drivers via CONFIG_ flags. The same upstream source file (drivers/net/ethernet/hisilicon/hns3/.c) may therefore appear in some artifacts and not in others. Microsoft’s public statement confirms Azure Linux contains the file; absence of a similar statement for another product is simply a lack of attestation, not proof of absence.

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What Microsoft actually says (and what that language practically guarantees)​

Microsoft’s FAQ wording used across many MSRC update pages follows a predictable pattern: Azure Linux is called out as a product that includes the implicated open‑source library and is therefore “potentially affected,” and Microsoft notes that it began publishing machine‑readable CSAF/VEX attestations in October 2025 and will update the CVE mapping if other products are identified. The practical takeaway is that Microsoft has performed an inventory sweep for Azure Linux and attested its status; Microsoft will expand that mapping (and publish attackers/impact notes) if additional product carriers are discovered. That inventory‑first approach is transparent but incremental.

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Cross‑referencing the public record (what independent sources show)​

To avoid over‑reliance on any single source, the CVE and patch were cross‑checked against multiple public records:

• The NVD entry for CVE‑2024‑26881 records the description and kernel call trace showing the NULL dereference in hclge_ptp_get_rx_hwts; that entry captures the technical root cause and severity classification.
• Distribution notices (Ubuntu, Debian security pages) list the vulnerability, the upstream summary text, and the distribution‑specific package updates or kernel versions that include the fix; Ubuntu’s security entry reports a CVSS score consistent with an availability impact.
• Kernel mailing‑list postings and the upstream patch series (LKML / spinics / lkml archives) document the author, the commit message, and the exact guard added to avoid dereferencing a NULL ptp pointer, making the code changes and rationale auditable. These are the authoritative upstream artifacts for the fix.
• OSV/other vulnerability aggregators compile the same description and publish a consolidated record suitable for tool ingestion and scanning.

Together, these records confirm the defect, the patch, and the mapping that Microsoft published for Azure Linux. They also support the conclusion that Microsoft’s public attestation is a product‑specific inventory statement rather than a statement about all Microsoft kernel artifacts.

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Practical impact and attack surface​

• Impact type: Denial of service (kernel crash) when the NIC receives a PTP/1588 packet that sets a timestamp flag and the driver attempts to access a missing ptp device pointer. This is not an arbitrary remote code execution vector, but it does produce immediate host instability.
• Required conditions:
• The kernel must include the hns3/hclge driver code (the driver is not present in all kernels).
• The host must be attached to hardware using HIP08‑family NICs (HiSilicon HIP08 SoCs or NICs that expose HNS3 functionality).
• PTP/1588 traffic must be received and processed such that the RX timestamp valid bit is set while the driver’s ptp pointer is NULL.
• Likelihood in public clouds: cloud providers typically deploy a mix of NIC vendors; many public cloud server fleets use Broadcom, Mellanox (NVIDIA), Intel, or vendor‑specific NICs rather than HiSilicon HIP08 parts. That reduces the chance that a random public cloud VM or general‑purpose Azure host would see this specific defect. However, specialized hardware (ARM server platforms, vendor‑specific appliances, on‑premise servers using Kunpeng/HIP08 SoCs) are the primary risk zone. This hardware‑dependence is why inventory mapping is essential. This is an area where Microsoft’s Azure‑specific attestation is especially helpful: Azure Linux images used on Azure‑managed hardware are the ones MSRC has verified. Where customers run Azure Linux images on physical hardware with HIP08 NICs, the risk is real unless kernels are patched.

Caveat: it is difficult from public data to enumerate every Microsoft product’s kernel config and exact upstream commit range. That is precisely why Microsoft’s FAQ language avoids claiming exclusivity — only an exhaustive artifact inventory can do that, and vendors publish those attestations on a per‑product cadence. If you require absolute certainty for a given Microsoft artifact (for example, a WSL shipping kernel or a specialized VHD image), confirm via the vendor’s VEX/CSAF attestation or by querying the binary for the presence of the driver object.

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How defenders and administrators should respond (practical checklist)​

If you run or manage Linux systems — especially on ARM/HiSilicon platforms or using Azure Linux — follow this prioritized set of actions:

• Inventory first: determine whether your kernel image includes the hns3/hclge driver.
• On a running system, check for loaded modules and on‑disk driver objects:
• lsmod | grep -i hns3
• modinfo hns3 (or modinfo hclge)
• find /lib/modules/$(uname -r) -type f -name 'hns3' -o -name 'hclge'
• If the driver is built into the kernel (not a module), check the kernel config:
• zcat /proc/config.gz | grep -i HNS3
• grep -i hns3 /boot/config-$(uname -r)
• If the presence of the driver is confirmed, escalate to patching.
• Patch promptly: install vendor or distribution kernel updates that include the upstream hns3 fix.
• Use your distro’s security update channels; Ubuntu, Debian and other mainstream distros already list the CVE and provide kernel updates or backports.
• Temporary mitigations if a patch is not immediately available:
• If hns3 is a loadable module and you are not using the affected NIC, unload and blacklist the module:
• sudo modprobe -r hns3
• echo "blacklist hns3" | sudo tee /etc/modprobe.d/blacklist-hns3.conf
• If the driver is built into the kernel, node isolation or removal of the relevant NIC (if feasible) are the only practical short‑term options until a patched kernel is applied.
• Consider firewalling or otherwise preventing PTP/1588 frames from reaching affected NICs where feasible (PTP typically uses layer‑2 multicast frames or UDP/319‑320; network segmentation can reduce exposure). Note: network filtering is only a partial mitigation because hardware might see and mark timestamps before filtering in some designs.
• Validate after remediation:
• After applying a patched kernel, confirm the absence of the vulnerable code by checking kernel version, module timestamps, and by re‑running the inventory checks above.
• For cloud images, consult the vendor’s VEX/CSAF attestation or the MSRC update‑guide mapping for the CVE to confirm the product is listed as remediated.
• For large environments and managed service vendors:
• Integrate the CVE into your vulnerability‑management tooling and correlate the CVE ID with artifact inventories and kernel build metadata so you can quickly identify which images or node pools are affected.
• Utilize machine‑readable VEX/CSAF attestations when available to automate per‑artifact assessments. Microsoft has committed to publishing these attestations as of October 2025; consume them via your vulnerability‑management pipeline where supported.

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Why Microsoft named Azure Linux specifically — and what it doesn’t prove​

Microsoft named Azure Linux in the CVE mapping because the company’s inventory process identified that the Azure Linux distribution includes the upstream source in question. This is an important, constructive disclosure practice: vendors should tell customers which managed products are definitely carriers of affected components so customers can prioritize patching and risk assessment.
That naming does not prove exclusivity for two reasons:

• Microsoft ships multiple, independently built Linux artifacts across products and services (Azure Linux images, WSL2 kernels, specialized appliance kernels, AKS node images). Artifact contents vary by kernel version and build configuration.
• The same upstream source can appear or be omitted depending on kernel config flags, so two Microsoft products might differ even if they both are “Linux kernels.” Consequently, Microsoft needs an artifact‑by‑artifact inventory; publishing “Azure Linux includes this library” is the accurate minimal statement that helps customers today while Microsoft completes broader inventory work.

In short: Microsoft’s attestation is useful and authoritative for that product; it is not — and deliberately cannot be — a universal guarantee of absence across every Microsoft kernel artifact. Treat the statement as an index result, not a universal clause.

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Risk assessment: who should care most?​

• High priority: operators of physical or virtual systems that use HiSilicon HIP08‑family NICs (for example, Kunpeng‑based servers or appliances where HNS3 drivers are the intended driver). These environments can see an immediate kernel crash if the hardware receives 1588/PTP frames in the problematic code path.
• Medium priority: Azure Linux customers and cloud tenants who run on Azure‑provided images where Microsoft has attested the library’s presence. Microsoft’s attestation makes it critical for those customers to confirm patch status of their Azure Linux images or node pools.
• Lower priority (but non‑zero): general Windows customers, WSL2 users, or operators of Microsoft infrastructure who assume “Microsoft said Azure Linux, so Windows/WSL/etc. are safe.” That assumption is risky: the only safe conclusion is to inspect the specific artifact(s) you run. If you operate WSL, an appliance, or a bespoke Microsoft image, verify the presence or absence of the driver in that particular kernel artifact rather than rely on a short MSRC FAQ sentence.

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How vendors (including Microsoft) can make these attestations more useful​

The security community has been pressing vendors to publish machine‑readable per‑artifact attestations (CSAF/VEX) so customers and toolchains can automatically map vulnerabilities to specific binaries and images. Microsoft announced a structured rollout of CSAF/VEX attestations and began publishing machine‑readable attestations in October 2025; that data makes it materially easier to answer the question “Which Microsoft artifacts include the affected source?” without manual inspection. Until those attestations are fully populated, product‑scoped statements remain the pragmatic compromise.
Recommendations for vendor practice:

• Publish artifact‑level attestations (VEX/CSAF) as machine‑readable feeds that vulnerability scanners can consume.
• Provide a simple artifact‑search API for kernel component presence (e.g., “does image X contain drivers/net/ethernet/hisilicon/hns3?”).
• When hardware affinity limits the impact (e.g., a defect affects only discrete vendor NICs), state that explicitly so operators can scope mitigation by hardware platform as well as by software artifact.

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Conclusion and bottom line for administrators​

CVE‑2024‑26881 is a targeted kernel robustness fix for the Hisilicon hns3/hclge networking code that prevents a NULL pointer dereference when PTP/1588 timestamps are present but the ptp device structure is not registered. Upstream kernel commits, distribution advisories, and vulnerability aggregators document the issue and the fix; Microsoft has attested that Azure Linux includes the implicated open‑source library and is therefore potentially affected, but that attestation is product‑scoped and not a categorical statement about other Microsoft artifacts. If you run Azure Linux, HiSilicon HIP08 hardware, or any kernel that may include the hns3 driver, inventory your systems, apply the vendor or distribution kernel patch, or use temporary mitigations (module blacklisting or NIC isolation) until patched kernels are deployed. For broader Microsoft artifacts (WSL2 kernels, special images), do not assume absence — verify each artifact via the methods outlined above or via vendor VEX/CSAF attestations when available.

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Source: MSRC Security Update Guide - Microsoft Security Response Center