CVE-2025-58185: Azure Linux Attestation Is Not Exclusive to Microsoft Products

Microsoft’s public attestation that the Azure Linux distribution “includes the implicated open‑source library and is therefore potentially affected” is accurate — but it is not a technical guarantee that Azure Linux is the only Microsoft product that could include the vulnerable component.

Background / Overview​

The defect tracked as CVE‑2025‑58185 is a memory‑exhaustion vulnerability in Go’s encoding/asn1 parsing logic that can cause large allocations when parsing maliciously crafted DER payloads. The core issue is that the parser allocated memory before fully validating incoming DER, enabling an attacker to present a small-but-crafted DER blob that expands into heavy allocations and drives a process to OOM. The vulnerability affects Go releases that predate the upstream fixes released in the Go 1.24.x and 1.25.x series. Microsoft has published a machine‑readable CSAF/VEX attestation covering the Azure Linux Distribution and explicitly stated that Azure Linux “includes the implicated open‑source library and is therefore potentially affected,” adding that the company will update the CVE attestation if impact to additional products is identified. That attestation is an inventory statement for a single product surface, not an exhaustive declaration about every Microsoft product or image.
This article explains what Microsoft’s wording means in practice, why Azure Linux being named does not imply exclusivity, where the vulnerable code can appear in Microsoft or third‑party artifacts, and what Windows and Azure administrators should do right now to measure and mitigate exposure.

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Why the wording from Microsoft matters — and what it does not mean​

Microsoft’s public messaging and VEX/CSAF attestation for Azure Linux are valuable because they provide an authoritative, machine‑readable inventory for that specific product. For customers running Azure Linux images, the attestation removes ambiguity about whether Microsoft has validated and published the status for that image.
However, the attestation is an iterative, product‑by‑product inventory process. Publishing a VEX artifact for one product does not automatically prove that other Microsoft products do or do not include the same open‑source component. Microsoft has stated it will update the CVE entry if additional product impact is found — which is consistent with standard vendor practice for complex supply‑chain issues. In short: the attestation documents what Microsoft has validated to date, not everything Microsoft sells.
Key takeaway: treat Microsoft’s attestation as authoritative for Azure Linux. For other Microsoft SKUs — WSL kernels, Marketplace images, appliance firmware, Azure Kubernetes Service node images, management agents, and any statically‑linked binaries — independent inventory and verification are still required.

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Technical scope: where this library appears and how the vulnerability propagates​

Understanding where a Go stdlib parser ends up in an ecosystem is crucial to assessing blast radius.

• The vulnerability is in the Go standard library package encoding/asn1. Any software written in Go and compiled with an affected Go toolchain that relies on encoding/asn1 (directly or indirectly, via crypto/x509, ocsp, or other helpers) can be impacted.
• The vulnerability can manifest in functions such as asn1.Unmarshal, x509.ParseCertificateRequest, and ocsp.ParseResponse — i.e., anywhere DER is read from an untrusted source.
• The practical exploit is a denial‑of‑service via memory exhaustion rather than direct remote code execution. The attacker’s objective is to trigger massive allocations and crash or stall the target process.

Where the vulnerable parsing occurs matters more than the presence of the library alone. Services that parse certificates, CSRs, OCSP/CRL responses, S/MIME messages, or other externally submitted DER blobs represent the highest‑value targets.

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Why Azure Linux being named does not equal “only Azure Linux”​

There are four strong, technical reasons the Azure Linux attestation cannot be read as a universal absence statement for all Microsoft products:

• Build‑time variance and per‑artifact choices
  Each Microsoft product or image is built with its own toolchain and packaging choices. Some images may include the Go toolchain as a system package; others may contain precompiled, statically‑linked Go binaries that embed the stdlib at build time. A distribution‑level update (e.g., updating the system go package) does not automatically replace static Go binaries baked into appliances or images.
• Multiple, separate Linux artifacts and node images
  Microsoft ships and manages many distinct Linux artifacts: Azure Linux images, Marketplace images, AKS node images, kernel packages, WSL kernels and images, container base images, and more. Each artifact is a discrete candidate for including a vulnerable component. An attestation for one product doesn’t prove anything about these other artifacts.
• Statically linked Go binaries and third‑party images
  Because Go programs are commonly compiled statically, a vulnerable library version can be embedded directly in binaries distributed across many images and services. These baked‑in artifacts require a rebuild to remove the vulnerable code — patching the system’s golang package won’t change them. Vendor‑supplied marketplace images and third‑party appliances may also include such binaries.
• The long tail: marketplace images and partner artifacts
  Images published in Marketplace or by partners may lag in updates or use different dependencies. These can harbor vulnerabilities long after upstream fixes are released unless vendors proactively rebuild and republish.

Put plainly: Microsoft’s attestation is a useful starting point but does not obviate the need for a targeted inventory across any Microsoft artifacts you operate or consume.

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Practical areas to inspect inside Microsoft environments​

If you run Microsoft products or host workloads on Azure, prioritize the following artifact classes for immediate inventory and assessment:

• Azure Linux VM images and marketplace images you provision from Azure Marketplace. Start with the images Microsoft has attested (Azure Linux) and then expand to other images used in your environment.
• Containers and orchestration agents (containerd, image builders, CI runners) that unpack layers or process tar archives; these frequently include Go‑based tooling and runtimes. Cloud providers often ship container tooling built in Go.
• Management agents and telemetry collectors (for example, cloud agent binaries) that may be built in Go or embed Go‑built third‑party tooling. Vendor agents are often distributed as compiled binaries and must be rebuilt or replaced to include upstream fixes.
• Custom or third‑party appliances that run on Azure or are published in Marketplace. Treat these as independent SKUs that need vendor validation.
• Any code or service that consumes DER payloads from untrusted sources — certificate upload endpoints, ACME/PKI tooling, CRL/OCSP processors, and email/TLS termination pipelines. These are the highest‑priority attack surfaces.

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Operational action plan — prioritized and practical​

The following checklist is ordered by what most organizations will need to do first. Each step is short, practical, and repeatable.

• Inventory: find where DER parsing or Go‑stdlib code runs in your estate
• Run SBOM scans and SCA tooling across repositories and artifacts. Add node scans for compiled Go binaries (strings, ldd, or runtime introspection where possible).
• For container images, scan layers for go binaries or inspect manifests and package lists. Focus first on publicly reachable services.
• Confirm patched Go versions where applicable
• The upstream remediation is included in the Go releases: patch versions in Go 1.24.x and 1.25.x series (for example, 1.24.8 and 1.25.2 were published to address this family of issues). Upgrade build toolchains and recompile artifacts where feasible.
• Rebuild static Go binaries and redeploy images
• If binaries were produced with an affected Go release, rebuild them with patched Go and redeploy. For Marketplace or third‑party appliances, open vendor tickets requesting rebuilt images or patched releases.
• Apply compensating controls where immediate patching is not possible
• Add input validation and reject suspect DER payloads at the ingress layer (WAF, reverse proxy, or application gateway).
• Enforce rate limits and parsing timeouts; sandbox any DER processing in constrained processes with memory quotas to limit blast radius.
• Detection and monitoring
• Look for process OOM events, repeated crashes, or high memory usage in services that process DER.
• Add telemetry around “x509 parsing” or “asn1.Unmarshal” failure paths. Capture incoming DER blobs that trigger exceptions for forensic analysis.
• Coordinate with Microsoft and third‑party vendors
• Subscribe to Microsoft’s CSAF/VEX attestation feeds for automated updates. Microsoft has committed to expanding CVE attestations if further impact is identified; continue to monitor those feeds.
• Post‑patch verification
• After updating, validate end‑to‑end behavior for certificate handling, CSR processing, and OCSP responses. Run regression tests and monitor logs for the new errors introduced by patched libraries.

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How to interpret Microsoft’s “we will update the CVE” promise​

Microsoft’s pledge to update a CVE attestation if additional products are found to be affected is a positive operational commitment: it means they will run inventories for other product SKUs and publish machine‑readable mappings when new product impact is validated. This makes automated vulnerability management more practical for customers who ingest vendor VEX/CSAF feeds.
Caveat: vendor attestation cadence varies. Until Microsoft publishes specific attestations for a product you rely on, you should assume the possibility of exposure and either (a) confirm absence via your own artifact inspection, or (b) treat the item as potentially affected and apply compensating mitigations while awaiting vendor confirmation.

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Threat model and exploitation likelihood​

This vulnerability’s primary impact is availability: a small, crafted DER payload can trigger large memory allocations and crash or severely degrade a verifying process. Public telemetry and scoring show a moderate CVSS and relatively low EPSS at publication, but the exploitation complexity is low if an attacker can reach the parser. That combination calls for urgent prioritization of externally facing systems and high‑availability services. Two points to keep in mind:

• Low EPSS today does not mean the vulnerability won’t be weaponized later. Availability bugs are often exploited quickly once proof‑of‑concepts or scanners appear.
• The real operational risk depends on whether untrusted DER reaches parsing code. Internal, fully trusted certificate workflows are lower risk than public APIs that accept user‑submitted certificates, CSRs, or formatted PKI artifacts.

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What administrators should tell their teams and vendors right now​

• For platform teams managing Azure Linux VMs: apply Microsoft’s published fixes and validate images against the vendor attestation for Azure Linux. Microsoft’s attestation is actionable for that product.
• For teams running other Microsoft products or Marketplace images: do not assume absence. Inventory the images and binaries you run, query vendors for attestation, and escalate to Microsoft if you find Microsoft‑branded artifacts that include compiled Go artifacts built with affected Go versions.
• For teams using third‑party appliances and vendor‑supplied binaries: open support cases with vendors, request rebuilds or patched firmware, and treat these items as high priority if they process DER inputs.
• For developers: pin and update the Go toolchain used in CI to the patched Go releases (for example, 1.24.8 or 1.25.2 where the fixes were backported) and recompile releases. Add parsing limits where libraries allow and perform fuzzing on DER/ASN.1 inputs as a defensive measure.

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Strengths in the vendor response — and remaining gaps​

Strengths

• Microsoft’s use of machine‑readable CSAF/VEX attestations for Azure Linux is a concrete transparency improvement that simplifies automation and prioritization for customers running that image.
• Upstream Go maintainers produced targeted fixes and published patch releases for the affected Go versions in the 1.24.x and 1.25.x series. Those releases are the canonical remediation path for any code built from source with an affected toolchain.

Remaining gaps and risks

• Vendor attestations cover validated product mappings only; they do not automatically span all Microsoft images, appliances, or third‑party artifacts. Customers continue to own per‑artifact inventory and risk validation.
• The long tail of statically‑linked binaries, marketplace images, and third‑party firmware will likely require coordination and take time to fully remediate. Those items often need vendor rebuilds or explicit patches.
• Public proof‑of‑concepts and scanning tools can appear quickly for trivially exploitable availability bugs; delays in rebuilding and redeploying patched artifacts increase operational risk.

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Final assessment and clear recommendations​

• Is Azure Linux the only Microsoft product that includes the vulnerable open‑source library? No — Microsoft has attested Azure Linux as one product that includes the implicated library and is therefore potentially affected, but that attestation is a statement about the inventory Microsoft has completed so far, not a comprehensive statement that no other Microsoft product includes the vulnerable component. Treat the attestation as authoritative for Azure Linux while continuing to inventory and validate other Microsoft artifacts you run or consume.
• What to do next (top priorities)
• Confirm whether any of your deployed Microsoft images or Microsoft‑distributed binaries contain Go‑built artifacts compiled with an affected Go release. If so, rebuild or replace with patched payloads.
• Update build toolchains (CI) to the patched Go versions and recompile release artifacts; do not rely solely on runtime package updates for statically‑linked binaries.
• Apply ingress‑level input validation and sandboxing for DER parsing endpoints where a rapid rebuild is not immediately possible.
• Monitor vendor VEX/CSAF feeds (including Microsoft’s) for updates and verify any new product attestations as they are published.

Microsoft’s attestation program makes patch prioritization easier for customers running Azure Linux. It does not, however, replace a customer’s responsibility to inventory their own deployed artifacts — especially when compiled languages like Go produce static binaries that can be distributed widely across images and services. Treat the vendor attestation as one authoritative data point, and combine it with your SBOMs, runtime telemetry, and targeted vendor inquiries to ensure your estate is actually protected.

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This article has synthesized the vendor attestation language and the technical details of CVE‑2025‑58185 to present a clear, operational view: Azure Linux is confirmed as a potentially affected Microsoft product, but it is not technically accurate to conclude that Azure Linux is the only Microsoft product that could include the vulnerable open‑source library. Continue to prioritize inventory, rebuilding with patched Go toolchains, and applying ingress hardening for DER‑processing endpoints until vendor attestations and your own verification demonstrate otherwise.

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Source: MSRC Security Update Guide - Microsoft Security Response Center