Azure Linux Attestation for CVE-2025-38213: What It Covers and What It Doesn't

Microsoft’s short product‑mapping for CVE‑2025‑38213 is accurate for the artifacts it covers — but it is not a universal safety guarantee for every Microsoft product. The CVE identifier for a kernel vgacon bug was eventually marked rejected by its CNA, while dozens of downstream distributors and vendors published fixes or advisories referencing the upstream kernel commits. Microsoft’s public wording — that “Azure Linux includes this open‑source library and is therefore potentially affected” and that the company began publishing machine‑readable CSAF/VEX attestations in October 2025 — is a product‑level attestation. It tells Azure Linux users to treat Microsoft’s Azure Linux images as in‑scope for remediation, and it commits Microsoft to update those attestations if other Microsoft products are later found to ship the same upstream code. Crucially, it does not prove other Microsoft artifacts cannot contain the same vulnerable component; organizations must still verify the images and binaries they run.

Background: what happened with CVE‑2025‑38213​

CVE‑2025‑38213 was raised in mid‑2025 to track a kernel issue in the vgacon (virtual console) code path. Automated testing (Syzkaller/KASAN reports) highlighted a slab out‑of‑bounds read around the vgacon_scroll/vcs_scr_readw code in drivers/tty/vt/. Upstream kernel maintainers merged safety checks that validate the vc_origin range in vgacon_scroll and related fixes to prevent the out‑of‑bounds access; those commits are available in the kernel stable trees that distributors pick up.
Within the CVE system the record for CVE‑2025‑38213 was later marked as rejected or withdrawn by the assigner. A “REJECT” in the CVE program is an administrative status that means the identifier is not to be used as a live CVE record; reasons vary — duplicate IDs, an eligibility decision (not a security issue), or a request/withdrawal by the original requester or CNA. At the same time, a broad set of Linux distributors and vulnerability trackers (Debian, Ubuntu, SUSE, Red Hat derivatives, Amazon Linux, and multiple commercial trackers) created advisories and mapping entries anchored to the upstream kernel commits and to corresponding packaging changes in their kernels.
That dual outcome — upstream code fixed and distributors publishing advisories* while the CVE ID itself shows REJECTED — is unusual but not unprecedented. It highlights two separate processes that converge around public vulnerability handling: the engineering fix in upstream projects and the administrative tracking (CVE allocation and final disposition).

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What Microsoft’s MSRC wording actually means​

When Microsoft’s Security Response Center (MSRC) writes a short FAQ line — “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability” — that sentence performs a clear, limited job:

• It is an authoritative attestation for the Azure Linux family that Microsoft has inspected and mapped the relevant upstream component in the Azure Linux artifacts it controls.
• It is not a global statement about every Microsoft product or image. Microsoft’s VEX/CSAF rollout deliberately started with Azure Linux in October 2025, and the MSRC language explicitly says Microsoft will update the CVE/VEX entries if additional Microsoft products are later identified as shipping the same component.

Put simply: the MSRC line is a yes for Azure Linux users — they should treat Azure Linux images that match the attested builds as in‑scope. It is not a no for all other Microsoft products.
Why Microsoft has taken this approach is operationally straightforward: a vendor‑side inventory and per‑product attestation model is much more reliable and automatable than a single sweeping public claim about all artifacts the vendor produces. Microsoft’s phased rollout of CSAF/VEX allows the company to publish machine‑readable, actionable attestations for a product family it has completed inventorying, then expand coverage as more inventories complete.

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Why “attested” does not equal “exclusive” — technical realities​

There are three practical technical reasons a single product attestation cannot be read as an exclusion for all other vendor artifacts:

• Kernel builds differ. The presence of a particular upstream source file or code path in a shipped binary depends on the exact kernel version, the commit range used, and the kernel configuration flags (CONFIG_*). Microsoft builds different kernels for different products (Azure Linux kernels for cloud images, linux‑azure kernels for VM host images, WSL2 kernels distributed in certain Windows features, and appliance or marketplace images). Each build is an independent artifact.
• Packaging and backports vary. Distributors sometimes backport fixes or ship different patch sets. A Microsoft image that uses a patched/older kernel or a downstream backport may or may not carry the same vulnerable code even if another Microsoft image does.
• Distribution of code moves across supply chains. The same open‑source code can be present in SDKs, container images, device firmware, or embedded appliances. A per‑product attestation is authoritative for that product’s artifacts, but the same file may be present in another artifact produced by a different team or pipeline.

Because of these realities, an attestation for Azure Linux is operationally vital — and simultaneously insufficient by itself to exclude exposure across the full set of Microsoft artifacts an organization may run.

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What “REJECTED” means (and what it does not mean)​

A CVE marked “REJECT” is an administrative signal: the CVE entry in the public CVE list is not to be used. Reasons include duplicates, a determination that the reported issue is not a security vulnerability, or a withdrawal by the CNA/caller. Important follow‑ups:

• REJECT does not inherently mean the underlying code change is unimportant. Upstream maintainers can — and often do — merge correctness and robustness fixes that distributors will still package and ship; those fixes deserve careful attention regardless of CVE status.
• Distributors and vendors may still publish advisories and ship patches tied to the upstream commits. In this case, multiple Linux vendors and distributors issued kernel updates citing the same upstream commit(s) and describing the change as a fixed issue in vgacon_scroll. Treat the engineering fix and the vendor advisories as the operational truth for systems that you manage.
• For managed images and vendor‑provided artifacts, a CVE REJECTED status does not absolve vendors from communicating per‑product impact. Microsoft’s attestation for Azure Linux and the promise to update VEX/CSAF records addresses that communications gap.

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Practical guidance: what customers should do now​

• If you run Azure Linux images (Microsoft‑published, curated images)
• Act on Microsoft’s attestation. Microsoft’s VEX/CSAF output and the Azure Linux advisory are authoritative for Azure Linux. Prioritize updating the affected Azure Linux images or apply the updated kernel packages Microsoft published.
• Verify the attested build numbers. Consume the CSAF/VEX attestation to find the exact kernel build(s) Microsoft marked as “Known Affected” or “Fixed” and map those to your deployed images.
• If you run other Microsoft‑provided Linux artifacts (WSL, Marketplace images, container base images from Microsoft, appliance images)
• Do not assume exclusion. Treat these artifacts as unattested until proven otherwise.
• Request VEX/CSAF or SBOMs. Ask your Microsoft support or account team for a per‑artifact attestation or an SBOM for the specific image. Microsoft’s public commitment to expand VEX/CSAF means they will update records when they identify additional affected products.
• Perform artifact‑level checks. For each image or appliance you use, run binary/package inspection or SBOM checks to identify if the vulnerable kernel code (or the specific driver/module) is present.
• For on‑premises or hybrid environments where the kernel is controlled by you
• Patch the host kernel promptly. Containers share the host kernel; therefore, even if a container image is safe, an unpatched host kernel is a system‑level exposure.
• Use distro vendor updates. Apply the vendor kernel updates from your distribution (Red Hat, SUSE, Debian/Ubuntu, etc.) that include the upstream fix.
• For cloud and ephemeral fleets (scale‑sets, autoscaling)
• Automate image rebuilds and redeploys. Rebuild golden images with the patched kernel and rotate instances. Use automation to avoid drift.
• Scan images for vulnerable package versions. Integrate image scanning into CI/CD and supply‑chain pipelines.
• For security teams and vulnerability managers
• Treat MSRC attestations as authoritative scoped inputs. In automated triage, mark Microsoft‑attested Azure Linux artifacts as needing remediation and create separate verification workflows for other Microsoft artifacts.
• Maintain an inventory and SBOM practice. The only scalable way to know whether a given artifact contains a particular open‑source component is to have SBOMs or to perform reproducible binary/package inspection.

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How to verify presence of the kernel code — concrete steps​

Below are practical verification steps you can run in typical environments. Adjust for your environment and privilege model.

• Identify the kernel version and build on a Linux system:
• uname -a
• cat /proc/version
• Check for the vgacon driver or related modules:
• If vgacon is compiled as a module, check lsmod | grep vgacon or modinfo vgacon.
• If built‑in, inspect the kernel config (typically /boot/config-$(uname -r) or /proc/config.gz if enabled) for CONFIG_VGACON or related flags.
• Inspect package versions:
• On Debian/Ubuntu: dpkg -l | grep linux-image
• On RHEL/CentOS: rpm -qa | grep kernel
• Map kernel package to vendor advisory numbers:
• Use your distribution’s security tracker/packaging metadata to map your kernel package version to the vendor advisory that references the upstream fix.
• For virtual machines or images provided by Microsoft:
• Retrieve the image’s metadata (image SKU and build number). Cross‑reference the Azure Linux VEX/CSAF attestation to confirm whether that SKU/build is in the “Known Affected” list.
• For fleets and many images:
• Use automation (Ansible, Salt, Chef, or platform APIs) to collect uname outputs and installed kernel package versions across the fleet.
• Compare them against a “known affected builds” list (from vendor advisories or the upstream commit mapping).
• For container workloads:
• Remember: containers share the host kernel. Verify the host kernel, not the container image, for kernel code exposure.

(Adapt these steps to your environment’s tooling. If you require exact commands for your distro/version, standard package manager queries above will apply.)

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Risk analysis — who is most affected and why​

• Attack surface: The vgacon issue is a local kernel bug; exploitation generally requires local code execution or a local unprivileged process that can interact with virtual console code paths. Many cloud environments and production images do not expose virtual console devices to tenant workloads, reducing exploitability in many cases.
• Privileges required: The majority of tracker analyses characterize the impact as requiring local privileges or guest‑adjacent access. That reduces immediate remote exploitation risk but does not eliminate severity for multi‑tenant or shared environments.
• Distribution reach: Because the vgacon code is in the kernel mainline and historically present across many kernel versions, multiple downstream distributors mapped fixes into their kernel packages. Vendors therefore treated the engineering fix as an availability/robustness issue and issued kernel updates accordingly.
• CVE REJECTED administrative effect: Some security teams may deprioritize CVE‑tagged work when an ID is rejected. That would be a mistake here — treat the engineering fix and vendor advisories as your operational signal rather than the CVE number alone.
• Supply‑chain considerations: The bigger operational lesson is supply‑chain visibility. Vendors publishing CSAs/VEX attestations and SBOMs for images reduces customer effort to triage. Microsoft’s phased VEX rollout for Azure Linux is a positive development; customers should demand the same openness for other artifacts they depend on.

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Strengths and limitations of Microsoft’s approach​

Strengths

• Authoritative product‑scoped attestation. Microsoft’s Azure Linux attestation provides a deterministic, machine‑readable signal that security teams can automate into triage.
• CSAF/VEX adoption. The decision to publish CSAF/VEX attestations improves machine‑readable transparency and enables automation across security tooling.
• Commitment to expand. Microsoft publicly committing to update VEX records if more products are identified as carriers is the right operational posture.

Limitations / Risks

• Phased rollout creates blind spots. Starting with Azure Linux reduces immediate ambiguity for that product, but absence of attestations for other product lines remains a blind spot until inventory completes.
• Dependency on consumer verification. Until attestations are broadly available across all Microsoft artifacts, customers must still perform artifact‑level checks and demand SBOMs.
• Perception risk: A “REJECTED” CVE plus a vendor attestation can confuse automated scanners and playbooks if those systems treat CVE presence/absence as the only triage signal.

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Action checklist for administrators (quick, operational)​

• For Azure Linux: verify attested builds → update images → redeploy.
• For Microsoft images (WSL, Marketplace, Azure Marketplace VM SKUs): request VEX/CSAF or SBOMs for each SKU; scan artifacts.
• For host kernels: patch hosts promptly; treat containers as dependent on host kernel.
• For CI/CD: integrate SBOM generation and image scanning into your pipeline; treat vendor attestations as high‑priority input.
• For governance: document a process to map vendor attestations to remediation tickets automatically.
• For auditing: capture vendor VEX/CSAF files and store them alongside your asset inventory for audit trails.

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Conclusion — the practical, defensible answer​

Is Azure Linux the only Microsoft product that includes the open‑source library and is therefore potentially affected by CVE‑2025‑38213? No — it is the only Microsoft product Microsoft has publicly attested (so far) to include the implicated upstream component. Microsoft’s wording and the company’s October 2025 CSAF/VEX rollout are deliberate: they give Azure Linux users a clear, authoritative remediation signal while promising to expand coverage as Microsoft completes inventory across other product families.
For defenders, the right operational posture is straightforward and unchanged by administrative CVE statuses: treat vendor attestations as authoritative for the named product, verify all other vendor artifacts you run using SBOMs, per‑artifact inspection, and aggressive patching of host kernels where containers run. The upstream kernel commits and downstream vendor advisories are the engineering source of truth; the CVE administrative flag is secondary. Prioritize remediation for attested Azure Linux images, and run a quick, automated inventory of all Microsoft artifacts in your environment so you can confirm whether those artifacts carry the affected code — and if they do, update them without delay.
Follow the attestation, verify the artifacts, and make SBOMs and VEX consumption a standard part of your vulnerability triage workflow — that is the only scalable way to turn a single product attestation into fleet‑wide safety.

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Source: MSRC Security Update Guide - Microsoft Security Response Center