The Linux kernel Global File System 2 (GFS2) just earned a new CVE — CVE‑2025‑38659 — for a defect described upstream as “No more self recovery,” and Microsoft’s initial public position names the Azure Linux distro as a confirmed shipper of the affected code while stating it will update the record if additional Microsoft products are found to include the library. That Microsoft statement is accurate so far, but it’s incomplete context for defenders: Azure‑branded kernels and cloud images — not just a single “Azure Linux” SKU — are the most likely Microsoft‑distributed carriers of GFS2, and other Microsoft distributions or kernel builds could include it as well. This feature unpacks what CVE‑2025‑38659 is, exactly which Microsoft products are plausibly at risk today, how to verify exposure on your hosts, remediation steps, and the operational risks to prioritize.
GFS2 is the Linux kernel’s clustered filesystem: it lets multiple nodes mount the same block device and coordinate access with a distributed lock manager. That clustering code sits in kernel space and is inherently sensitive — filesystem parsing and journal recovery paths run with full kernel privilege, and small errors can produce host‑wide crashes or worse.
CVE‑2025‑38659 was assigned for a specific upstream change that removed an attempted “self‑recovery” path in GFS2 after maintainers concluded the local replay logic was wrong and unsafe. The bug’s public description explains that when a node withdraws but is the only one with the filesystem mounted, GFS2 attempted to replay the local journal; during that control flow gfs2_recover_func dereferenced sdp->sd_jdesc->jd_inode — historically leading to a use‑after‑free and, more recently, to a NULL‑pointer dereference. The upstream remedy was to remove the self‑recovery attempt entirely rather than attempt fragile local journal replay. This is a kernel robustness bug in filesystem recovery code. Public trackers and vendors characterize the impact as a denial‑of‑service (kernel oops/panic) risk rather than a confirmed remote code‑execution primitive; distributors assign it medium severity in several advisories, and vendor package maintainers are issuing kernel updates and backports to address the fix in stable series.
Key references used in this analysis include the NVD/OSV vulnerability descriptions, Ubuntu and SUSE distribution advisories calling out Azure‑targeted kernel packages, and Microsoft’s public MSRC advisory comments and WSL kernel repository notes — these independent sources align on the technical facts and on the appropriate operational response (inventory, patch, validate).
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / overview
GFS2 is the Linux kernel’s clustered filesystem: it lets multiple nodes mount the same block device and coordinate access with a distributed lock manager. That clustering code sits in kernel space and is inherently sensitive — filesystem parsing and journal recovery paths run with full kernel privilege, and small errors can produce host‑wide crashes or worse.CVE‑2025‑38659 was assigned for a specific upstream change that removed an attempted “self‑recovery” path in GFS2 after maintainers concluded the local replay logic was wrong and unsafe. The bug’s public description explains that when a node withdraws but is the only one with the filesystem mounted, GFS2 attempted to replay the local journal; during that control flow gfs2_recover_func dereferenced sdp->sd_jdesc->jd_inode — historically leading to a use‑after‑free and, more recently, to a NULL‑pointer dereference. The upstream remedy was to remove the self‑recovery attempt entirely rather than attempt fragile local journal replay. This is a kernel robustness bug in filesystem recovery code. Public trackers and vendors characterize the impact as a denial‑of‑service (kernel oops/panic) risk rather than a confirmed remote code‑execution primitive; distributors assign it medium severity in several advisories, and vendor package maintainers are issuing kernel updates and backports to address the fix in stable series.
Why Microsoft mentioned "Azure Linux" — and what that means
Microsoft’s initial public statement about CVE‑2025‑38659 named Azure Linux (the Microsoft‑curated Linux distribution and associated Azure kernel packages) because the Azure cloud kernels and images are the most obvious Microsoft‑owned pieces that carry the Linux kernel, and because Azure packaging routinely includes kernel builds and modules targeted at the cloud. That is a conservative and transparent first disclosure: Microsoft will add other products to the advisory if further inventorying shows other Microsoft products ship the affected code. Independent distribution advisories show the same pattern: when a kernel‑level GFS2 fix lands upstream it commonly appears in vendor kernel builds and cloud‑targeted kernels. Canonical’s Azure‑targeted kernel package (linux‑azure / linux‑azure‑6.x) is explicitly listed in Ubuntu security notices that reference GFS2 fixes for Azure kernels, demonstrating that cloud‑targeted kernel packages are a real distribution vector for this filesystem code. Similarly, enterprise Linux vendors package Azure‑targeted kernel modules (for example, gfs2‑kmp‑azure on SUSE or kernel packages annotated with "azure" in multiple vendor changelogs). Those vendor artifacts show that Microsoft’s cloud kernels are a distinct distribution pathway for filesystem modules such as GFS2. In short: when Microsoft says "Azure Linux," they are pointing at the kernel builds and cloud images Microsoft publishes for Azure VMs — and those kernel artifacts are a primary Microsoft surface where GFS2 lives.Short answer to the user’s question
- Is Azure Linux the only Microsoft product that includes the GFS2 code and is therefore potentially affected?
- No — Azure Linux (and the Azure‑targeted kernel packages / kernel‑azure builds) are the primary Microsoft distribution surface that includes GFS2, but they are not necessarily the only Microsoft‑branded builds or packages that can contain the code. Other Microsoft‑distributed kernel builds targeted at cloud VMs (kernel‑azure / linux‑azure packages used by vendors for Azure images) are part of the same family, and any Microsoft product that publishes or distributes a Linux kernel build could include the GFS2 code depending on kernel config and packaging choices.
- Is Windows (desktop/server) itself affected?
- No — Windows desktop/server SKUs do not include the Linux GFS2 kernel module. However, Microsoft ships Linux kernels in other places (for example, the WSL2 kernel and Azure kernel packages) and those are the places to check.
- Is WSL/WSL2 affected?
- The default Microsoft WSL2 kernel is a Microsoft‑maintained Linux kernel build; historically, it has shipped with a limited set of features and with many drivers built in or omitted depending on the configuration. WSL2’s kernel historically did not include a modules directory by default and module support was limited, although more recent WSL kernel releases added module support. Whether a specific WSL kernel build contains GFS2 depends on that build’s kernel configuration (CONFIG_GFS2) and the modules that Microsoft chose to include. That is a host‑level check — it cannot be answered globally without inspecting the running kernel or the particular WSL kernel build version.
Cross‑checked facts and independent sources
To be methodical, the public technical description of CVE‑2025‑38659 and the upstream fix are recorded in multiple independent vulnerability trackers and vendors’ advisories:- The National Vulnerability Database (NVD) and OSV reflect the upstream description of the bug and note the null‑pointer / use‑after‑free symptom and the upstream fix.
- Multiple distributions have published advisories and package backports listing azure‑branded kernel packages as consumers of the fix — for example, Ubuntu’s security notices for linux‑azure and SUSE’s gfs2‑kmp‑azure packaging list GFS2 fixes in the Azure kernel lineage. That demonstrates the real distribution path for the vulnerable code into cloud VM images.
- Distribution trackers (Debian, Amazon Linux, Red Hat channels) show which kernel releases were vulnerable and where fixes have been landed or backported — these pages are the practical source of deployment guidance for administrators. Use those vendor pages to map CVE→fixed‑package→fixed‑version for your platform.
Practical detection: how to check whether a given Microsoft‑delivered host is carrying GFS2
Because presence depends on the kernel config and packaging choices, the only reliable way to determine exposure on any individual host is to inspect that host’s kernel and installed packages. Use the following checks on Linux hosts (run as root or with sudo):- Check whether the GFS2 module is present as a module or built into the kernel:
- If modules exist:
- modinfo gfs2 || echo "no gfs2 module found"
- If /proc/config.gz is available:
- zcat /proc/config.gz | grep -i GFS2
- If /boot/config-$(uname -r) exists:
- grep -i GFS2 /boot/config-$(uname -r)
These commands tell you whether the kernel was built with CONFIG_GFS2 set (either built‑in or module) or whether a gfs2.ko file exists for the running kernel. - Check if gfs2 is registered with the kernel:
- grep gfs2 /proc/filesystems
- lsmod | grep gfs2
- dmesg | grep -i gfs2
If gfs2 is present or has been attempted to load, these locations will record it. - Check distro / cloud‑image packaging:
- Ubuntu/Debian:
- dpkg -l | egrep 'linux-azure|kernel-azure|linux-image-azure'
- RHEL/SLES/SUSE:
- rpm -q kernel-azure gfs2-kmp-azure gfs2-kmp-default
- Azure images often use packages named linux‑azure / kernel‑azure or provide "linux‑azure" builds in official images; those package names in your package database are a strong indicator that you are running an Azure‑targeted kernel.
Remediation and mitigation guidance
- Patch the kernel with vendor updates
- Follow your distribution or cloud vendor’s guidance to install the patched kernel packages that include the upstream GFS2 fix, then reboot into the patched kernel.
- For Azure Linux VM images, apply the linux‑azure / kernel‑azure package updates provided by Microsoft or the downstream distribution maintainer and reboot.
- Many vendors are shipping fixes as kernel backports; check your vendor advisory for the exact package and fixed version number.
- Use kernel livepatch where available
- If a livepatch kernel backport is available for your distribution (and your environment allows it), apply vendor livepatch updates to reduce reboots on critical systems while you plan maintenance. Confirm the livepatch includes the GFS2 change before assuming protection.
- Isolate workloads and limit attack surface
- If you run cluster filesystems in multi‑tenant or cloud contexts, ensure that only trusted nodes can access underlying shared block devices and that network / storage isolation prevents untrusted actors from presenting crafted images that could trigger the recovery code.
- Detection / monitoring
- Add instrumentation to collect kernel oops/panic messages and alert on filesystem recovery traces referencing gfs2_recover_func or gfs2 journal messages. Hunt for recent oops in /var/log/kern.log, journalctl -k, or equivalent telemetry channels.
- Validate and document
- After patching and rebooting, validate the running kernel release (uname -r) and re‑run the detection commands to ensure the vulnerable code path is no longer present on the running kernel.
- Stay tuned to vendor advisories
- Microsoft’s MSRC statement commits to transparency and to publishing CSAF/VEX content for Azure Linux and other Microsoft‑shipped Linux artifacts; rely on vendor KBs and package changelogs to map CVE→fix. If Microsoft updates the CVE to name additional Microsoft products, adjust your inventory accordingly.
Special note on WSL and other Microsoft Linux surfaces
- WSL2: Microsoft publishes the WSL2 kernel source and configuration files in a public GitHub repository; the exact kernel features enabled in the shipped WSL kernel depend on Microsoft’s config and the release tag. Historically, the WSL kernel did not expose a full /lib/modules tree and many modules were compiled statically; more recent WSL kernel releases reintroduced module support and made module packaging available. Whether a particular WSL kernel contains GFS2 is therefore a build‑time decision and must be verified by inspecting the WSL kernel config (zcat /proc/config.gz inside WSL) or examining the WSL kernel build. If you are using a custom WSL kernel, that kernel’s .config determines the presence of GFS2. Do not assume WSL is automatically vulnerable or automatically safe; check each kernel build.
- Azure kernel packages vs. downstream vendor kernels: Many distributions produce Azure‑branded kernel builds (linux‑azure, kernel‑azure, gfs2‑kmp‑azure). Those packages are the canonical Microsoft distribution channel for kernel code in Azure VMs and are the most likely Microsoft artifacts to carry GFS2. If you consume Azure Marketplace images (Ubuntu on Azure, SLES on Azure, etc., the vendor images often rely on a linux‑azure kernel or include specific modules built for Azure, which is why vendor advisories list azure‑branded package names when upstream kernel issues land.
Risk analysis: exploitation model and severity
- Attack vector and privileges required
- The GFS2 defect lies in a filesystem recovery path executed in kernel context. In practice, exploitation requires mounting or interacting with a crafted GFS2 image or block device and may require local privileges or the ability to cause the kernel to process a malicious image. Several public trackers and vendors categorize the resulting impact as denial‑of‑service (kernel oops / panic) rather than unauthenticated remote code execution. That said, the presence of memory‑corruption primitives in kernel code can sometimes be a foothold for privilege escalation when additional conditions align; treat kernel filesystem faults as high‑priority to patch even when remote RCE is not yet demonstrated.
- Operational impact
- A kernel panic on a cloud VM that hosts business‑critical services has immediate availability consequences. For multi‑node clusters that share block devices, a carefully constructed attack could target storage presented to many nodes; for single‑node mounts the practical attack surface is smaller but still material for hosts that mount untrusted images. The practical severity is therefore context‑dependent: for cloud providers and shared storage hosts it moves toward higher urgency.
- Likelihood of widespread exploitation
- So far (public record as of this writing) there are no widespread PoCs weaponizing this CVE in the wild; multiple vendors are shipping patches and the public advisories emphasize fixes and backports. Nevertheless, the correct operational posture is immediate inventory and patching for exposed hosts.
Step‑by‑step checklist (for administrators)
- Inventory:
- Run detection commands (see above) across your fleet to identify hosts whose kernel packages or running kernels include GFS2. Use configuration management tooling to centralize results.
- Map to vendor advisories:
- For each affected host, map the exact kernel package and version to vendor advisories (Ubuntu USNs, SUSE advisories, Red Hat or Microsoft Update Guide entries) and identify the fixed package versions you must install.
- Patch and reboot:
- Schedule kernel package updates and reboots (or apply livepatch where appropriate). Validate the running kernel afterwards.
- Harden and monitor:
- Restrict which workloads can mount or access raw block devices. Increase kernel log monitoring for gfs2-related messages and for kernel oops traces.
- Document and report:
- Track the CVE in your vulnerability management system and record remediation status. If you use Azure, watch Microsoft’s MSRC updates and the CSAF/VEX feeds they publish for machine‑readable status updates.
Outstanding uncertainties and cautions
- Microsoft’s MSRC statement is deliberately conservative: it confirms Azure Linux as a carrier and promises to update the CVE if additional Microsoft products are identified. At the time of writing, the precise enumeration of all Microsoft products that embed GFS2 has not been globally published by Microsoft. That means defenders should not assume only a single SKU is affected — inventory every Microsoft‑provided Linux kernel build that you run (linux‑azure packages, WSL kernels, any appliance or image Microsoft supplies) and verify by checking the running kernel or packages. Microsoft’s binding advisory updates will be authoritative; until then, vendors’ distribution advisories and upstream kernel commits are the reliable technical evidence to act on.
- Whether WSL includes GFS2 in the default Microsoft WSL kernel is not a single global fact; it depends on the precise WSL kernel version shipped in a given Windows build or on the custom kernel selected by the user. Check each running instance.
Conclusion
CVE‑2025‑38659 is a kernel‑space GFS2 repair that removes an unsafe self‑recovery path and corrects a dereference that could crash a host. Microsoft’s first public attribution to Azure Linux is correct in identifying the most obvious Microsoft distribution surface carrying the affected code, but it’s not a complete inventory of every Microsoft‑supplied Linux kernel build or package that could contain GFS2. Administrators must therefore treat all Microsoft‑distributed Linux kernel builds they run — especially linux‑azure / kernel‑azure packages and any Azure image kernels — as candidates for exposure until confirmed patched. WSL kernels should be checked individually because module inclusion is a build‑time decision. Use the detection commands and vendor‑mapped package updates described above, prioritize patching of cloud and shared‑storage hosts, and monitor MSRC and your distribution vendors for CSAF/VEX and package advisories as they become available.Key references used in this analysis include the NVD/OSV vulnerability descriptions, Ubuntu and SUSE distribution advisories calling out Azure‑targeted kernel packages, and Microsoft’s public MSRC advisory comments and WSL kernel repository notes — these independent sources align on the technical facts and on the appropriate operational response (inventory, patch, validate).
Source: MSRC Security Update Guide - Microsoft Security Response Center
