CVE-2024-6119 OpenSSL: Is Azure Linux the only Microsoft product at risk?

A surprisingly small parsing bug in a widely used cryptography library has forced cloud operators and Linux admins to ask a blunt question: when Microsoft says “Azure Linux includes this open‑source library and is therefore potentially affected,” does that mean Azure Linux is the only Microsoft product at risk? The short answer is no — Azure Linux is the one Microsoft product that has been explicitly attested as including the affected OpenSSL components, but the practical reality is broader: the vulnerable code lives in OpenSSL, a dependency widely embedded across Linux distributions, container images, and product artifacts, and other Microsoft‑shipped Linux artifacts can — and in some documented cases do — include the same library. This feature unpacks CVE‑2024‑6119, explains why Microsoft’s wording matters (and where it doesn’t), assesses which Microsoft artifacts are plausibly affected, and lays out concrete detection and remediation steps for defenders.

Background / Overview​

CVE‑2024‑6119 is a denial‑of‑service (DoS) vulnerability in OpenSSL’s X.509 name‑checking routines. The bug is triggered when an application performs certificate name checks — for example, a TLS client checking that a server certificate matches an expected DNS name, IP address, or email address — and the certificate contains a malformed otherName entry in its Subject Alternative Name (SAN) extension. Under those conditions, certain OpenSSL code paths can dereference malformed buffers and read past an available buffer length, which may crash (abort or segfault) the calling process.
OpenSSL acknowledged the issue in its security advisory and issued fixes in the 3.x branch family. The vulnerability’s impact is availability (application termination) rather than confidentiality or integrity, but the operational fallout can be significant for services and automated clients that rely on uninterrupted TLS client behavior.

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What the vulnerability actually does​

• The bug occurs during name matching functions such as X509_check_host(), X509_check_ip(), and X509_check_email(), which iterate SAN entries and compare them against an expected name supplied by the caller.
• If a SAN entry of type otherName is present and contains malformed ASN.1 length data or a buffer shorter than the declared length, the OpenSSL comparison logic may use the declared length without validating buffer bounds.
• The result is an out‑of‑bounds read that typically causes an immediate application crash. The crash is not a memory disclosure or remote code execution primitive — it is an availability problem (DoS).
• Because the bug only surfaces when callers explicitly ask OpenSSL to perform name checks, servers that only validate certificate chains (signatures, validity dates) without performing name matching are much less likely to be affected in practice. Many TLS servers also do not perform name checks against a supplied reference identifier, which reduces server‑side exposure relative to clients.

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What vendors and distributions did (and why Microsoft’s message matters)​

OpenSSL released fixes (the 3.x series patches), and major Linux distributors and infrastructure vendors subsequently shipped updates or advisories mapping the CVE to their packaged OpenSSL. Linux‑focused vendors — Red Hat, Oracle Linux, FreeBSD distributions, and numerous cloud distro projects — published advisories and updates. Microsoft’s security response guide entry for this CVE takes a product‑level stance: Microsoft has confirmed that Azure Linux includes the implicated OpenSSL components and is therefore potentially affected; Microsoft also said it will update the CVE mapping if additional Microsoft products are identified.
That MSRC wording is important and intentionally scoped: it is an authoritative inventory statement for a named product family (Azure Linux). It is not a negative claim that other Microsoft artifacts cannot include the same library. In plain terms:

• If you run Azure Linux images, treat that product as in‑scope and prioritize patching according to Microsoft’s guidance.
• If you run other Microsoft‑supplied Linux artifacts (CBL‑Mariner images, Azure Marketplace appliances, WSL distributions provided by vendors, managed Linux containers used by Azure services), you cannot assume absence — you must verify.

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Is Azure Linux the only Microsoft product that includes OpenSSL?​

No. Azure Linux is the Microsoft product Microsoft has publicly attested to as including the vulnerable OpenSSL components. However:

• Microsoft’s own Linux distributions (historically CBL‑Mariner and the newer Azure Linux family) include standard system packages such as OpenSSL. Security scanning data and vendor plugin mappings show both Azure Linux and CBL‑Mariner packages tied to OpenSSL CVE updates, confirming the library’s presence in those Microsoft Linux artifacts.
• CBL‑Mariner was explicitly developed by Microsoft for cloud infrastructure and edge scenarios and has been used as the basis for Azure Linux. That means multiple Microsoft Linux artifacts share lineage and can carry the same packaged libraries.
• Beyond Microsoft’s Linux distributions, many Microsoft cloud offerings run or rely on Linux‑based components (VM images, containers, appliance images, monitoring/agent binaries, etc.). Those components may be built from upstream distributions or custom images that include OpenSSL.
• Microsoft Windows desktop and server products use the native Windows TLS provider (Schannel) for many platform services and do not ship OpenSSL as a core TLS provider; therefore, native Windows TLS stacks are not generally impacted by this OpenSSL vulnerability. However, any Windows‑hosted applications that bundle OpenSSL (third‑party tools, packaged appliances, or custom app bundles) could still carry the library and require inventory.

In short: Azure Linux is a confirmed carrier; other Microsoft Linux artifacts are plausible carriers and some (Mariner‑line artifacts used inside Microsoft infrastructure) have been specifically identified in third‑party scanning. Microsoft’s statement does not mean it’s the exclusive carrier.

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Evidence and cross‑validation (what we checked)​

To make a defensible assessment we cross‑checked the following independent sources:

• OpenSSL security advisory and commit history describing the bug, the affected versions (OpenSSL 3.0, 3.1, 3.2, 3.3 lines), and recommended fixed releases.
• Multiple vendor advisories and vulnerability databases (distribution advisories, security bulletins and scanning tool plugin pages) that map CVE‑2024‑6119 to distribution packages and list fixes for Azure Linux and Mariner line artifacts.
• Cloud and infrastructure vendor scanning databases (Nessus/Tenable plugin entries) that explicitly map Azure Linux and CBL‑Mariner packages to CVE‑2024‑6119 and to patched package versions.
• Microsoft’s own MSRC wording that Azure Linux includes the affected open‑source library and the subsequent note that Microsoft will update the CVE product mapping if additional impacted products are identified.

Those cross‑references show a coherent picture: OpenSSL coded bug → fixes released upstream → Linux distributors and cloud ISO/image vendors patched or listed OpenSSL in their security advisories → Microsoft explicitly attested Azure Linux while leaving open the possibility of further mappings.

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Practical implications for organizations using Microsoft products​

• Azure Linux customers: treat this as an actionable item. Microsoft’s attestation confirms that Azure Linux images may include an affected OpenSSL and that Microsoft intends to provide patch guidance. If you run Azure Linux, update the openssl packages to the fixed versions or apply the distribution security update Microsoft provides.
• Customers running CBL‑Mariner‑derived artifacts, Marketplace images, or Microsoft base images: do not assume they are unaffected. Build artifacts and container images inherited from Mariner or Azure Linux may carry the same vulnerable packages unless explicitly patched.
• Native Windows servers and endpoints: for built‑in Windows TLS consumers (services that rely on SChannel), this CVE is not directly relevant. However, Windows hosts can still run third‑party applications or Linux containers that bundle OpenSSL — those components must be inventoried and patched.
• Managed Azure services: many first‑party Azure services are multi‑tier and include Linux components. Customers using managed services should rely on Azure’s published guidance and expect the service operator (Microsoft) to patch server‑side components where applicable. Where you host your own workloads on Azure VMs or AKS nodes, the responsibility is yours to patch guest images and container images.

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How to determine whether a given Microsoft artifact is affected (detection checklist)​

Use the following steps to inventory and detect presence of affected OpenSSL versions across your Microsoft artifacts and endpoints. These steps are practical, short, and focused on producing verifiable evidence.

• Inventory Linux images and artifacts
• Enumerate all Linux images, base OS versions, and container images in your estate (Azure Marketplace images, AKS node pools, VM images, custom gallery images).
• Use automated image‑scanning tools (container image scanners, package inventory tooling) to list installed package names and versions.
• Check package versions (RPM/Debian)
• For RPM‑based Microsoft variants (CBL‑Mariner/Azure Linux), run:
• rpm -qa | grep -i openssl
• For Debian/Ubuntu‑style guests, run:
• dpkg -l | grep -i openssl
• Verify whether installed OpenSSL packages match or predate the fixed upstream versions.
• Check linked shared libraries for running processes
• For a running Linux process suspected of using TLS, run:
• lsof -p <pid> | grep libcrypto
• ldd /path/to/binary | grep libcrypto
• This identifies whether a given process is dynamically linked against OpenSSL libraries present on disk.
• Inspect container images
• Pull and scan container images for openssl package artifacts. Use:
• docker run --rm -it <image> rpm -qa | grep openssl
• or use image scanners (Snyk, Trivy, Clair) to enumerate CVEs.
• Prioritize images running in production, sidecars, and init containers.
• Search for bundled OpenSSL binaries on Windows hosts
• Many Windows applications bundle a native openssl.dll (for example, 3rd‑party monitoring agents or embedded open source tools). Search program files or vendor directories for common OpenSSL artifacts and verify their versions.
• Use telemetry and vulnerability scanners
• Ensure your vulnerability scanning infrastructure (Nessus, Qualys, Microsoft Defender for Cloud, etc.) is current and includes CVE‑2024‑6119 detection. Validate that the scanner’s mappings include both the distribution package and the specific OpenSSL version thresholds.

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Concrete remediation steps (prioritized)​

• Patch OpenSSL where it appears in base OS or container images
• Upgrade to the OpenSSL releases that include the fix (apply the distribution’s security update that contains the upstream OpenSSL patch).
• The general fixed versions are in the 3.x family as provided by upstream and backported by distros; apply vendor‑supplied package updates rather than attempting manual source builds unless you maintain bespoke images.
• Replace or rebuild container images
• If container images include vulnerable OpenSSL packages, rebuild images from patched base layers, re‑publish, and perform a rolling redeploy.
• For third‑party images you consume, request patched images from the vendor or mitigate by running them behind TLS‑terminating proxies.
• For Windows hosts: patch/bundle updates for applications that include openssl binaries
• If third‑party software on Windows bundles OpenSSL, look for vendor updates or apply a vendor‑approved patch. Consider isolating or hardening the service until a patch is applied.
• Temporary mitigations if patching cannot be immediate
• Where feasible, avoid performing remote name matching in client code — i.e., if you control the client application, use stricter input validation or perform certificate identity checks using safer APIs or validated parsing code. This is often impractical but may be possible in custom clients.
• Use TLS termination or a proxy that validates and sanitizes certificates before they reach vulnerable downstream clients.
• Rate‑limit or filter abnormal certificate sizes at inbound gateways to reduce risk of crafted certificates being delivered to vulnerable clients — this is a coarse and imperfect mitigation.
• Monitor for crashes after patching
• Because the vulnerability manifests as a crash, watch for new or unexplained TLS client process terminations, core dumps, or service restarts.
• Tighten observability around TLS clients: add process‑level monitoring and alerting on application terminations and crashes.

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Operational detection examples and quick checks​

• Determine OpenSSL package version on a Mariner/Azure Linux node:
• rpm -q openssl
• rpm -q openssl-libs
• Compare the reported versions against your distro’s security advisory to confirm whether the patched package has been installed.
• Check whether a running client binary is linked to OpenSSL:
• pid=$(pgrep -f <client_binary_name>)
• lsof -p $pid | grep libcrypto
• If the output shows libcrypto or libssl paths, that process uses OpenSSL and should be prioritized for testing/patching.
• For containers:
• docker run --rm --entrypoint '' <image> rpm -qa | grep openssl
• If you see openssl package names, rebuild the image with a patched base.

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Why Microsoft’s stated limitation is not a reason to be complacent​

Microsoft’s public CVE mapping practice — naming Azure Linux as a product that includes the implicated library — is transparency for the customers that run that product. But absence of attestation is not proof of absence. There are three reasons for this cautious posture:

• Microsoft ships many artifacts that embed or derive from Linux distributions (CBL‑Mariner‑derived images, marketplace appliances, cloud guest kernels). Each artifact has its own build configuration and package set; only explicit inventory or vendor attestation can confirm presence or absence of a library.
• Build configuration matters. Two kernels or two images built from the same upstream source can behave differently depending on configured features and backports.
• Vendor mapping processes take time. Microsoft committed to update CVE product mappings if additional impacted products are found; until that happens each customer must assume “not yet attested” means “needs verification.”

Treat Microsoft’s Azure Linux attestation as meaningful for Azure Linux customers — and treat everything else as something you must verify.

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Risk assessment and prioritization guidance​

• High priority:
• Production services that act as TLS clients and perform certificate identity checks against arbitrary external servers (for example, automation bots that connect to untrusted services, API clients consuming third‑party HTTPS endpoints, scheduled jobs that download data from remote servers).
• Containerized workloads with many outbound TLS client flows where a client crash would cause service instability.
• Multi‑tenant systems where one compromised tenant could present malicious or crafted certificates to another tenant’s client process.
• Medium priority:
• Standalone TLS servers that rarely check client identity; their exposure is typically low for this vulnerability.
• Windows‑native services using Schannel as the TLS stack (these are not directly affected), but still verify third‑party software that bundles OpenSSL.
• Low priority:
• Systems that never perform certificate name checks or do not use OpenSSL in their stack.

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Guidance for Microsoft customers and security teams​

• Don’t assume global safety because only one Microsoft product is named. Use the detection checklist to find affected artifacts in your environment.
• If you run Azure Linux images: follow Microsoft’s update guidance and schedule a patch window. Azure Linux customers get the most direct mapping and should be the first to remediate.
• If you rely on Azure Marketplace images, managed node pools, or Microsoft‑provided base images for containers, treat those images as potential carriers until you have verified the package inventory.
• Make use of CSAF/VEX or vendor attestations where available. Microsoft’s commitment to publish CSAF/VEX for Azure Linux provides machine‑readable evidence; request the same level of attestation for other Microsoft product families you rely on.
• Keep an eye on service telemetry for sudden TLS client crashes or unexplained restarts. The bug’s signature is abrupt process termination during certificate validation.

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Broader takeaways and risk control lessons​

• Open‑source supply‑chain inventory is not optional. Vulnerabilities in ubiquitous libraries inevitably cross product boundaries. A single upstream issue affects every product that embeds a vulnerable version.
• Product‑level attestations are useful but incomplete. Microsoft’s attestation for Azure Linux is necessary and helpful, but defenders must build artifact‑level inventory and automated scanning pipelines to close the gap.
• Don’t conflate library presence with exploitability. This particular CVE is a DoS (crash) vector that requires specific certificate constructs and name checks to trigger. Remediation priority should consider the typical certificate handling patterns in your clients and services.
• Bake observability into client code. Crashes in client processes are easier to detect and correlate if process lifecycle telemetry and alerting are already in place.

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Conclusion​

CVE‑2024‑6119 is an operationally relevant OpenSSL denial‑of‑service that highlights the perennial challenge of composing and maintaining secure software from common building blocks. Microsoft’s public statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is a precise and useful inventory signal for Azure Linux customers — but it is not an exclusive claim. Other Microsoft Linux artifacts (CBL‑Mariner lineage images, Azure Marketplace and container images, and any Microsoft artifact that bundles or depends on OpenSSL) can also carry the vulnerable code and must be inventoried, scanned, and patched.
Action for defenders is straightforward: inventory, detect, and patch where OpenSSL 3.x instances or vendor packages are present; rebuild and redeploy container images that include vulnerable packages; and use Microsoft’s published product attestations (CSAF/VEX where available) to supplement, not replace, your artifact‑level verification. The vulnerability itself is not a remote code execution or data‑exfiltration issue, but the availability impact — abrupt client crashes — is enough to warrant prioritization for clients and automated systems that rely on stable TLS client behavior.

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Source: MSRC Security Update Guide - Microsoft Security Response Center