Microsoft’s concise MSRC line — “Azure Linux includes this open‑source library and is therefore potentially affected” — is accurate for the product Microsoft has inspected, but it should not be read as a categorical statement that only Azure Linux could include the vulnerable ksmbd code. The vulnerability tracked as CVE‑2025‑22042 is an upstream Linux kernel fix in the in‑kernel SMB server (ksmbd): the patch adds a missing bounds check for the “create lease context” code path. Multiple independent distribution and vulnerability trackers confirm the technical nature of the fix, its April 2025 disclosure date, and a mid‑range severity (CVSSv3 ≈ 5.5), and they show that exposure depends on which kernel build and configuration you run — not on vendor brand alone.
CVE‑2025‑22042 was published in April 2025 as a Linux kernel issue described in upstream commit messages and distro advisories as “ksmbd: add bounds check for create lease context.” The change is defensive: it inserts a bounds check to prevent an out‑of‑bounds access in the in‑kernel SMB/CIFS server implementation (ksmbd). The vulnerability is primarily an availability risk (kernel crash or OOPS) rather than direct data confidentiality loss, and many vendors assigned it a CVSSv3 base score around 5.5 (AV:L/AC:L/PR:L/UI:N, Availability impact: High).
ksmbd is part of the upstream Linux kernel tree. That matters because inclusion of the ksmbd code in any given product or image is a build‑time decision: it depends on the kernel version used, the kernel configuration options (for example CONFIG_KSMBD or related flags), and whether the vendor or distributor backported the upstream fix into their stable kernel branch. Distribution advisories (Debian, Ubuntu, Oracle, Amazon Linux, etc.) list affected kernel versions and patch guidance; these independent trackers corroborate the same upstream commit and the same remediation path.
Crucially, that attestation is not a warranty that every other Microsoft product has been scanned and found clear. The absence of a “Not Affected” attestation for a product simply means Microsoft has not yet published an inventory result for that product. Because Microsoft’s VEX/CSAF rollout is product‑by‑product, other Microsoft artifacts may remain un‑attested for some time. Treat MSRC’s Azure Linux mapping as a high‑priority signal for Azure Linux customers, and as informational for other Microsoft customers pending per‑artifact verification.
Key artifacts to check first:
However, the phased rollout means attestations will appear product‑by‑product. Until Microsoft publishes an explicit Not Affected attestation for a given product, absence of an attestation is an unknown, not proof of safety. Large vendors ship many distinct kernel artifacts; two kernels built from the same upstream tree can differ in enabled features and therefore in exposure. Operators must therefore treat Azure Linux attestation as definite for that product and perform artifact‑level checks for other Microsoft artifacts they run.
Operators should therefore combine two parallel tracks: (1) act immediately on Microsoft’s Azure Linux guidance, and (2) perform artifact‑level discovery, verification, and remediation for other Microsoft‑supplied kernels and images in their environment. Use SBOMs, kernel config inspections, module checks, and vendor VEX/CSAF attestations to close blind spots. This balanced approach reduces immediate risk for Azure Linux customers while preventing complacency that could leave other Microsoft artifacts exposed.
In short: Azure Linux is the only Microsoft product Microsoft has publicly attested so far for CVE‑2025‑22042 — and that attestation is authoritative for Azure Linux — but it is not a proof that Microsoft’s other products are safe. Treat the MSRC message as a high‑priority patching signal for Azure Linux, and run your own artifact verification across WSL, AKS, Marketplace images, and any Microsoft‑distributed kernels you consume.
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
CVE‑2025‑22042 was published in April 2025 as a Linux kernel issue described in upstream commit messages and distro advisories as “ksmbd: add bounds check for create lease context.” The change is defensive: it inserts a bounds check to prevent an out‑of‑bounds access in the in‑kernel SMB/CIFS server implementation (ksmbd). The vulnerability is primarily an availability risk (kernel crash or OOPS) rather than direct data confidentiality loss, and many vendors assigned it a CVSSv3 base score around 5.5 (AV:L/AC:L/PR:L/UI:N, Availability impact: High).ksmbd is part of the upstream Linux kernel tree. That matters because inclusion of the ksmbd code in any given product or image is a build‑time decision: it depends on the kernel version used, the kernel configuration options (for example CONFIG_KSMBD or related flags), and whether the vendor or distributor backported the upstream fix into their stable kernel branch. Distribution advisories (Debian, Ubuntu, Oracle, Amazon Linux, etc.) list affected kernel versions and patch guidance; these independent trackers corroborate the same upstream commit and the same remediation path.
What Microsoft’s MSRC statement actually means
The wording — product attestation, not exclusivity
Microsoft’s MSRC FAQ response for the CVE family follows a consistent pattern: it declares that Azure Linux includes the implicated open‑source component and is therefore potentially affected, and it explains Microsoft’s plan to publish machine‑readable CSAF/VEX attestations (a phased rollout that began in October 2025) and to update CVE mappings if further Microsoft products are identified as affected. This is an inventory attestation for Azure Linux — it confirms Microsoft has inspected that particular product family and found the upstream code that maps to the CVE.Crucially, that attestation is not a warranty that every other Microsoft product has been scanned and found clear. The absence of a “Not Affected” attestation for a product simply means Microsoft has not yet published an inventory result for that product. Because Microsoft’s VEX/CSAF rollout is product‑by‑product, other Microsoft artifacts may remain un‑attested for some time. Treat MSRC’s Azure Linux mapping as a high‑priority signal for Azure Linux customers, and as informational for other Microsoft customers pending per‑artifact verification.
Why Azure Linux is a confirmed priority — and why other artifacts still matter
- Azure Linux is the product Microsoft has explicitly checked and declared “potentially affected.” If you run Azure Linux images or kernels, you should prioritize applying the vendor updates Microsoft publishes for the distribution. That attestation gives Azure customers a clear operational priority.
- However, the same ksmbd code lives in upstream kernel source. Any Microsoft product or artifact that ships a Linux kernel built from a tree that includes the vulnerable commit range and whose kernel configuration enables ksmbd could, in principle, carry the vulnerability until patched. This includes:
- WSL2 kernel binaries distributed by Microsoft (the WSL2 kernel repo and its build configs are public, and inclusion depends on the chosen kernel config).
- linux‑azure kernels used in some Azure VM SKUs and curated Marketplace images.
- AKS node images or other Azure managed images that rely on Microsoft‑maintained kernels.
- Any Marketplace images or appliances Microsoft publishes where the kernel config enables ksmbd.
Technical anatomy of CVE‑2025‑22042
What the bug is (simple view)
The bug is a missing bounds check in ksmbd’s handling of the “create lease context” code path. Without the check, malformed or unexpected inputs could cause ksmbd to read or write beyond intended buffers, which may trigger kernel instability or crashes under certain conditions. Upstream maintainers merged a small patch that inserts the missing check; the fix is present in the stable kernel trees referenced by distribution advisories.Exploitability and impact
- Attack vector: local — an attacker must be able to interact with the ksmbd service or kernel interfaces on the host. This typically means local access or container access on a host where ksmbd is enabled.
- Privileges required: low (unprivileged) in theory, depending on service exposure and local user constraints.
- Primary impact: availability (kernel panic, OOPS, denial of service). Most advisories classify confidentiality and integrity impacts as none or negligible for this class of out‑of‑bounds in ksmbd.
- Whether ksmbd is enabled in the kernel (built‑in or loadable module).
- Whether ksmbd is listening or reachable from untrusted contexts (e.g., untrusted containers with host namespace access).
- Whether the host allows users or workloads that can send malformed SMB requests to the in‑kernel SMB server.
Who else could be affected — practical inventory checklist
Do not assume the vulnerability is limited to Azure Linux. Any Microsoft artifact that ships or runs a Linux kernel built with ksmbd enabled is a potential carrier. Operators should treat the Azure Linux attestation as a confirmed hit but perform artifact‑level discovery across their estate.Key artifacts to check first:
- WSL2 kernel packages and local WSL installations.
- Azure VM images (especially images labeled “linux‑azure” or “Azure Linux”).
- AKS node images and any Microsoft‑curated Marketplace images you run.
- Custom VM or container base images created from Microsoft images or build pipelines that reference Microsoft’s kernel trees.
How to verify whether a given Linux artifact includes ksmbd
Use the following practical checks on running systems and images:- On a running host
- Check the running kernel config:
- cat /boot/config-$(uname -r) | grep -i ksmbd
- zgrep -i KSMBD /proc/config.gz (where /proc/config.gz exists)
- Check loaded modules:
- lsmod | grep ksmbd
- grep -i ksmbd /proc/modules
- Look for ksmbd symbols in dmesg or /proc/kallsyms:
- dmesg | grep -i ksmbd
- For images or offline kernels
- Inspect the kernel config file shipped with the image (often under /boot or in image build artifacts).
- Search image build recipes for CONFIG_KSMBD, fs/smb/server or for the specific source files (fs/smb/server/auth.c) referenced in commit diffs.
- Compare kernel version and commit hash against the upstream fixes referenced by OSV/NVD and distro advisories.
- For WSL2 on Windows clients
- Microsoft publishes the WSL2 kernel source and build configs; inspect the kernel config used by your WSL channel or examine the binary’s embedded config where possible. If in doubt, treat WSL kernels as unverified until updated kernels / attestations are available.
Immediate mitigation and remediation guidance
If you manage Azure Linux images- Prioritize and apply Microsoft’s published kernel updates for Azure Linux as soon as they are released. Microsoft’s attestation makes Azure Linux a confirmed priority.
- Inventory → Verify → Patch:
- Inventory all Linux images, VMs, containers, and WSL kernels in your environment.
- Verify whether ksmbd is present (use the checks above).
- Patch affected kernels using distro or vendor updates; if you build your own images, rebuild with updated kernels that include the upstream fix.
- If you cannot immediately patch:
- Blacklist the ksmbd module (if ksmbd is modular and not required) by creating /etc/modprobe.d/blacklist-ksmbd.conf containing:
- blacklist ksmbd
- Rebuild initramfs and reboot if necessary so the module cannot be auto‑loaded.
- Restrict access to SMB ports on hosts that do not require SMB services (iptables/nftables rules, host firewalls).
- Use network segmentation to prevent untrusted workloads from reaching hosts that expose ksmbd.
- Monitor Microsoft WSL kernel release notes and update the WSL kernel binary when Microsoft publishes an updated build or attestation. Treat WSL kernels as a distinct artifact for verification; Microsoft’s VEX rollout will gradually expand attestations.
Detection and post‑remediation checks
After patching or blacklisting:- Inspect kernel logs (dmesg, journalctl -k) for OOPSes referencing ksmbd or fs/smb/server symbols.
- Confirm the kernel version and commit include the upstream fix by checking distro advisory package versions or the kernel commit range referenced by OSV/NVD.
- Re‑run artifact scans and SBOM reconciliation to ensure images redeployed to production contain the patched kernel or do not enable ksmbd.
- For availability incidents caused by repeated kernel panics or OOPSes, collect kernel crash dumps and analyze stack traces for ksmbd paths.
- If your threat model requires it (e.g., kernels processing sensitive cryptographic material via ksmbd paths), consider targeted forensic checks for residual secret data in freed pages — note this is specialist work and should be driven by clear indicators.
Why Microsoft’s phased VEX/CSAF approach helps — and its limits
Microsoft’s decision to publish CSAF/VEX attestations (starting October 2025) is an operational transparency improvement: it will let customers automate reconciliation and quickly determine which Microsoft products are Known Affected, Not Affected, Under Investigation or Fixed for specific CVEs. That model accelerates triage and reduces guesswork for the artifacts Microsoft has fully inventoried.However, the phased rollout means attestations will appear product‑by‑product. Until Microsoft publishes an explicit Not Affected attestation for a given product, absence of an attestation is an unknown, not proof of safety. Large vendors ship many distinct kernel artifacts; two kernels built from the same upstream tree can differ in enabled features and therefore in exposure. Operators must therefore treat Azure Linux attestation as definite for that product and perform artifact‑level checks for other Microsoft artifacts they run.
Risk analysis — strengths and potential risks
Strengths (what’s reassuring)
- The fix for CVE‑2025‑22042 is small, surgical, and merged into upstream stable kernels, making vendor backports straightforward.
- Independent tracking by multiple distros and vulnerability databases (Ubuntu, Debian, Amazon, Oracle/Snyk, OSV, NVD/OpenCVE) provides cross‑validation of the technical fix and severity rating. These independent confirmations reduce the chance of mischaracterization.
- Microsoft’s MSRC attestation for Azure Linux and its commitment to publish CSAF/VEX attestations improves transparency for customers of that product.
Risks (what to watch for)
- The vulnerability is in upstream kernel code; any kernel build that enables ksmbd can be affected. This introduces a supply‑chain risk that vendor product labels alone may not reveal.
- Microsoft’s attestation naming only Azure Linux does not mean other Microsoft artifacts (WSL2 kernels, linux‑azure kernels, AKS images, Marketplace images) are unaffected; those artifacts must be inventoried and verified individually. Relying solely on MSRC’s Azure Linux statement may leave blind spots.
- Some environments use custom or unmanaged Marketplace images and developer VMs whose kernel builds are not covered by vendor attestations; these often harbor the greatest operational exposure because they are overlooked by patch pipelines.
Action checklist (recommended operational steps)
- Prioritize Azure Linux hosts — apply Microsoft’s kernel updates for Azure Linux now.
- Inventory all Linux artifacts across your estate (VMs, containers, WSL kernels, AKS nodes, Marketplace images).
- For each artifact, verify whether ksmbd is enabled (kernel config, lsmod, /proc/modules).
- Patch or rebuild images that include vulnerable kernel versions; redeploy patched kernels.
- If immediate patching is impossible, blacklist ksmbd and restrict SMB exposure via network controls.
- Subscribe to MSRC VEX/CSAF feeds and distro advisories (Ubuntu, Debian, Red Hat, Oracle, Amazon) for confirmed fixed package versions.
- After remediation, validate no ksmbd OOPSes appear in kernel logs and confirm kernel commit or package versions include the upstream fix.
Final assessment and conclusion
Microsoft’s MSRC statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is factually correct and actionable for Azure Linux customers: if you run Azure Linux, treat your images and nodes as confirmed carriers and apply Microsoft’s updates. At the same time, the technical reality of the Linux kernel ecosystem — where the same upstream code can appear in many different kernel builds and images — means Azure Linux is very likely not the only possible Microsoft product that could carry ksmbd. Other Microsoft artifacts (WSL2 kernels, linux‑azure kernels for VM SKUs, AKS node images, Marketplace images) could be affected until they are individually inventoried and attested.Operators should therefore combine two parallel tracks: (1) act immediately on Microsoft’s Azure Linux guidance, and (2) perform artifact‑level discovery, verification, and remediation for other Microsoft‑supplied kernels and images in their environment. Use SBOMs, kernel config inspections, module checks, and vendor VEX/CSAF attestations to close blind spots. This balanced approach reduces immediate risk for Azure Linux customers while preventing complacency that could leave other Microsoft artifacts exposed.
In short: Azure Linux is the only Microsoft product Microsoft has publicly attested so far for CVE‑2025‑22042 — and that attestation is authoritative for Azure Linux — but it is not a proof that Microsoft’s other products are safe. Treat the MSRC message as a high‑priority patching signal for Azure Linux, and run your own artifact verification across WSL, AKS, Marketplace images, and any Microsoft‑distributed kernels you consume.
Source: MSRC Security Update Guide - Microsoft Security Response Center
