CVE-2024-22653: Yasm Patch and Microsoft Supply Chain Impact

A NULL-pointer dereference discovered in the Yasm assembler (tracked as CVE-2024-22653) is small in code but broad in consequence: the bug lived in a widely reused open-source component, was fixed in a targeted upstream commit, and — contrary to a narrow reading of a Microsoft FAQ — the presence of Yasm across multiple Microsoft-maintained Linux images means Azure Linux is not the only Microsoft distribution that can include this library. Administrators, build engineers, and security teams should treat this as a supply-chain patching item: identify where Yasm is present in your estate, prioritize updates on build hosts and container images, and validate that the patched upstream commit has been propagated into the specific package build your environment consumes.

Background / Overview​

Yasm is a portable assembler and a commonly used build-time dependency for multimedia and low-level toolchains. It is frequently invoked by projects that assemble hand-written machine-language fragments (for example, parts of FFmpeg or other codecs), and distributions ship it both as a runtime/development package and as a build-time tool.
The vulnerability reported as CVE-2024-22653 was publicly disclosed in late May 2025. The root cause is a NULL pointer dereference in the function yasm_section_bcs_append (file: libyasm/section.c) introduced by an earlier commit. The issue allows specially crafted inputs or invocation paths to cause Yasm to dereference a NULL pointer and crash, producing a denial-of-service against the process that invokes Yasm. The maintainers merged a focused fix upstream that adds a defensive NULL check; the fix is present in the upstream repository as a small commit that explicitly guards against appending to a NULL section.
From a risk standpoint the vulnerability is medium-severity for most victims: it does not directly permit code execution or data corruption in the way buffer-overflow exploits might, but it does permit reliable process crashes. For any system that uses Yasm in unattended build environments, CI/CD pipelines, or as part of hosted services, repeated or automated crashes can translate to meaningful availability and operational impact.

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The bug in technical terms​

What went wrong in the code​

At a high level, the function yasm_section_bcs_append(yasm_section [I]sect, yasm_bytecode [/I]bc) appended bytecode nodes to a section list. The vulnerable code assumed sect was a valid pointer in all execution paths where bc existed. When sect was NULL and the call still proceeded, the function attempted operations that dereferenced sect, which produced a segmentation fault.
The upstream fix is intentionally small and defensive: before attempting to use sect, the code now checks whether sect is NULL, logs a clear error message indicating an attempt to append to a NULL section, and returns early with a NULL result rather than continuing into unsafe memory access. That change addresses the crash mode without changing any functional behavior when proper inputs are provided.

Why this is exploitable (and why its impact is limited)​

• Exploitability: The flaw can be triggered by providing crafted input to a process that invokes libyasm/yasm in ways that exercise yasm_section_bcs_append. In many installations this requires local access or controlled input to a build process, which reduces remote-exploit risk compared with typical network-facing bugs. However, CI systems, automated build runners, container image builders, or services that accept user-provided source can present an attack surface.
• Impact: The primary impact is availability — crashes result in denial-of-service for the process using Yasm. There’s no public evidence that the defect enables arbitrary code execution. That said, denial-of-service in automated build systems can have substantial operational and business effects, especially if exploited at scale.

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What the upstream and downstream responses look like​

• Upstream fix: The Yasm project merged a small patch that adds the necessary NULL check and an error message. The commit is concise and straightforward.
• Distribution responses: Linux distributions and downstream consumers quickly tracked the issue. Multiple distro maintainers released package updates or rebuilds that include the upstream fix or a patched snapshot. Some repositories and distribution-specific advisories list patched package releases or rebuilt packages that incorporate the upstream commit.

This typical open-source lifecycle — discovery, upstream fix, downstream packaging and distribution — means the responsibility for mitigation is shared: upstream fixes the defect in source, but each downstream package maintainer must produce and ship updated packages for their distribution or product image.

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Who is affected: distributions, packages, and the Microsoft angle​

The broader ecosystem​

Yasm is packaged widely: Debian and Ubuntu package the assembler, Fedora issued advisories and updates, and multiple other Linux distributions have Yasm in their repositories. For developers and administrators this translates into two pragmatic realities:

• Yasm can be present on development and build hosts (installed via package managers like apt, dnf, or rpm).
• Yasm is often present in base images used for containers, CI runners, and minimal cloud images that are used to build or assemble binaries.

Because Yasm is both a runtime tool and a development tool, the places it appears are varied — from developer desktops to automated build farms, to container image build stages.

Microsoft’s published position (and why nuance matters)​

Microsoft’s Security Update Guide pages for Linux-related CVEs have, in multiple entries, included a standard FAQ paragraph that emphasizes the role of the Azure Linux (Azure Linux / CBL-Mariner) team in keeping the distro up to date with secure open-source library versions. That paragraph stresses transparency and references Microsoft’s move toward publishing machine-readable vulnerability metadata (CSAF/VEX).
However, a close look at package repositories and Microsoft-maintained Linux lines shows that the picture is not limited to one product or image:

• Microsoft maintains CBL-Mariner, the internal Linux distribution that underpins many of its cloud offerings and "Azure Linux" imagery. CBL-Mariner’s package repositories include Yasm packages — i.e., the assembler is present in the official Mariner package indexes and has received package updates over time.
• The CBL-Mariner distribution is used to build and power multiple Microsoft services and offerings: examples include EFLOW/Azure IoT Edge on Windows, certain Azure VM images and system components, and Microsoft’s internally-curated base images for cloud services. Because CBL-Mariner acts as the base for (or appears in) multiple product images, a vulnerable package in Mariner can translate into exposure beyond a single named product label.
• Microsoft’s security guidance correctly states their intent to report which Microsoft products include a vulnerable library. Their FAQ wording — that Azure Linux is the Microsoft product that includes the library and is therefore potentially affected — functions as a pragmatic short answer for customers who run the Azure Linux images. It does not amount to an exhaustive inventory of every Microsoft product or image that might include the same package via another Microsoft-maintained distribution.

In short: while Microsoft’s published Q&A emphasizes Azure Linux as the canonical Microsoft-maintained Linux distribution that receives these updates, the presence of Yasm in CBL-Mariner package repositories and the use of Mariner across several Azure and edge products demonstrates that the library is not confined strictly to a single product label. Practically, any Microsoft product or image that is built on or includes Mariner packages might have included the vulnerable version prior to being updated.

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Evidence and cross-checks (summary of findings)​

• The vulnerability is tracked as CVE-2024-22653 and described as a NULL pointer dereference in yasm_section_bcs_append introduced by a specific commit. The CVE and multiple third-party vulnerability databases and advisories record this description.
• Upstream Yasm merged a fix that guards against a NULL sect pointer by inserting a check and error return; this commit is small and reviewable.
• Multiple distributions and security advisories list CVE-2024-22653 and have published fixed package versions: Debian/Ubuntu trackers, Fedora advisories, and other distro sources show the vulnerability and patching activity.
• Microsoft package repositories for CBL-Mariner publicly list yasm package builds and versions. The Mariner package index includes yasm builds with timestamps indicating continued packaging and updates; these are the same distribution artifacts Microsoft uses for certain Azure images.
• Microsoft’s own Azure Linux / Mariner-related repositories and release notes have references to patching or packaging Yasm in the context of distro updates.

Taken together, these independent sources paint a consistent picture: the vulnerability existed upstream, a fix was added upstream, distributions and maintainers issued package updates, and Microsoft’s own Mariner repositories contain Yasm packages that should be updated or have been updated to incorporate fixes.

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Practical impact for enterprises and administrators​

Where to look in your environment​

• Build hosts: Search developer workstations and CI/CD runners for the presence of Yasm. It is often installed as a package (yasm) or appears in build toolchains used to compile media libraries.
• Container build stages: Yasm may be present in intermediate container images used to compile or link native artifacts. Even if final runtime images don’t include it, build-time images can be a vector for disruption.
• Base images and OS images: If you consume Microsoft-maintained images that are based on CBL-Mariner, Azure Linux, or other Microsoft-maintained distro images, those images may include the Yasm package in their package lists.
• Appliance and edge products: Microsoft’s EFLOW (Azure IoT Edge for Linux on Windows), Azure Batch images that reference Mariner, and other curated Microsoft images can include Yasm through the underlying package set.

To detect presence quickly, administrators can use these fast checks (examples — choose the command appropriate for your OS and environment):

• Debian/Ubuntu: query package lists for yasm (for example, dpkg -l | grep yasm) on runners and images.
• RPM-based systems: rpm -qa | grep yasm or dnf list installed yasm.
• Container images: inspect the package manifest or run the above commands inside ephemeral containers derived from builder images.

Suggested mitigation and remediation steps​

• Inventory:
• Identify all hosts, images, CI runners, and build containers that have yasm installed.
• Prioritize systems that are automated or externally accessible, and systems that run unattended build jobs.
• Patch:
• For host systems, use your distribution’s package manager to upgrade the yasm package to the fixed release published by the distributor.
• For containerized builds and CI images, rebuild images from updated base images or install the patched package in your build pipeline and regenerate artifacts.
• Validate:
• Confirm that the upstream fix (the defensive NULL-check commit) is present in the version your package manager installed, or that the package version corresponds to the distributor’s advisory that lists the fix.
• Run smoke tests of affected build processes and CI jobs to ensure the change does not break the assembler’s expected behavior.
• Monitor:
• Watch vendor advisories and Microsoft’s Security Update Guide entries for updates — Microsoft explicitly states they will update CVE records if impact to additional products is identified.
• If you rely on Microsoft-published images, track the Mariner and Azure Linux release notes and package repositories to know when patched builds are published.
• Short-term mitigations (where patching is delayed):
• Isolate build hosts from untrusted inputs and limit who can submit source that triggers assembler actions.
• Add CI job guards or sandboxing to reduce the blast radius of a crash (restart policies that don’t mask repeated failures may be appropriate so that an alert is raised).

Prioritization guidance​

• Highest priority: automated, high-volume CI systems and build hosts used to produce artifacts for production environments; these are likely to be used frequently and a crash could stall release pipelines.
• Medium priority: developer workstations and ephemeral developer clouds; impacts are local but can disrupt developer productivity.
• Lower priority: systems where Yasm is present but not actively invoked in production workflows.

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Why Microsoft’s FAQ answer can be misread — and what to do about it​

Microsoft’s published FAQ responses about Linux CVEs emphasize Azure Linux as the primary Microsoft-maintained Linux distribution for keeping open-source libraries up to date. This is a useful and generally accurate point for customers who consume official Azure Linux images.
However, the phrase “Is Azure Linux the only Microsoft product that includes this open-source library and is therefore potentially affected by this vulnerability?” followed by an explanation about Azure Linux can be read as asserting exclusivity — that only Azure Linux needs consideration. That reading is too narrow:

• Microsoft operates multiple Linux initiatives and images — CBL-Mariner is used across Azure services and edge offerings.
• The presence of the yasm package in Microsoft’s Mariner package indexes demonstrates that the library appears in more than a single named product family.
• Microsoft’s own operational model often reuses Mariner or curated Linux images across different product lines; therefore, a vulnerable package in the Mariner ecosystem can surface in multiple Microsoft products or offerings unless specifically excluded.

Practical takeaway: treat Microsoft’s FAQ as a helpful but not exhaustive inventory. Perform your own environment inventory to verify whether your managed images or services are built from or include Mariner/CBL-Mariner packages that contain Yasm.

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Recommendations for Microsoft customers and maintainers​

• Don’t assume a single product label (for example, “Azure Linux”) is the whole story. Confirm with inventory and package queries across all Microsoft-supplied images, appliances, and base images you use.
• For operators of CI/CD and build infrastructure, treat assemblers like Yasm as a high-priority maintenance item because their failure modes directly affect pipeline availability.
• If you consume Microsoft-curated images (for example, Azure Marketplace images or Azure VM images that list CBL-Mariner variants), check the image manifest or installed package list and confirm whether patched yasm packages have been applied. Rebuild or redeploy images as necessary.
• Rely on vendor advisories but validate them within your environment. Microsoft’s security communications will be authoritative for Microsoft-owned product packaging, but the distribution chain (upstream commit → distro package → image rebuild) creates timing gaps that you must manage.
• Add a validation gate to your CI pipelines that detects and fails the build when essential build tools crash or when builds exhibit unexpected assembler failures. This helps surface regressions introduced by a missing patch in a reproducible way.

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Final analysis — answering the user question directly​

Is Azure Linux the only Microsoft product that includes this open-source library and is therefore potentially affected by CVE-2024-22653?

• Short answer: No — Azure Linux is an important Microsoft-maintained Linux image and is explicitly targeted in Microsoft’s disclosure process, but it is not the sole Microsoft product or image that can include the Yasm library.
• Evidence and reasoning:
• Microsoft’s Mariner package repositories include yasm packages; CBL-Mariner (often referenced as Azure’s internal Linux distribution) is reused across multiple Microsoft offerings and serves as the base for several Azure and edge images.
• Upstream and distribution-level advisories indicate Yasm is widely packaged across the Linux ecosystem; Microsoft’s own distribution artifacts show Yasm builds and rebuilds, meaning that multiple Microsoft-managed images or services may have included the vulnerable package prior to being patched.
• Microsoft’s FAQ language is accurate in that Azure Linux / CBL-Mariner will receive updates and the company commits to transparency, but the FAQ is not a comprehensive inventory of every Microsoft product that might transitively include the same library via the Mariner package set.

In practice, the safest posture for customers is not to rely on the notion of “only Azure Linux is affected.” Instead, assume that any Microsoft-supplied image that uses the Mariner / Azure Linux package set, or that was built from a base image incorporating those packages, could contain the vulnerable yasm until you confirm a patched package version is present.

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Closing practical checklist for administrators (quick actionable items)​

• Inventory: Locate every host, VM image, container, and CI runner that could have yasm installed.
• Verify: For each instance, check the installed yasm version and confirm whether the package includes the upstream fix.
• Patch: Apply the distro vendor’s patched package or rebuild images from patched base layers that incorporate the upstream commit.
• Test: Re-run critical CI jobs and build tasks to validate operational continuity.
• Monitor: Subscribe to vendor advisories and Microsoft’s Security Update Guide updates; Microsoft will update CVE entries and publish CSAF/VEX metadata to help automation.
• Document: Record where patched and unpatched yasm packages exist to support audits and incident response.

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CVE-2024-22653 is a reminder that small code defects in low-level libraries ripple across supply chains. The fix upstream is small and low-risk, but getting that fix into every package and image that your organization consumes is the operational challenge. For Microsoft customers, treat Azure Linux guidance as a baseline but verify Mariner-based images and any other Microsoft-supplied artifacts in your environment — assume the library could appear in more than one product line until you have verified otherwise.

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Source: MSRC Security Update Guide - Microsoft Security Response Center