CVE-2025-58183 Go archive tar Unbounded Allocations and Azure Linux Attestation

A critical memory-allocation flaw in the Go standard library’s archive/tar package (tracked as CVE-2025-58183) can cause a Go program to perform unbounded allocations when parsing GNU pax-format sparse maps, producing an out-of-memory condition and a possible denial-of-service. Microsoft’s public attestation currently lists the Azure Linux Distribution as the product for which the company has published a machine-readable vulnerability status; Microsoft also says it will update that attestation if impact to other Microsoft products is identified. This article unpacks the technical details, evaluates the scope and risk to Microsoft customers, and provides practical, prioritized steps administrators and developers should take now to detect, mitigate, and remediate exposure.

Background: what the flaw is and why it matters​

The bug resides in the Go standard library’s archive/tar implementation. When reading a GNU pax 1.0 sparse map, the tar.Reader did not enforce a reasonable upper bound on the number of sparse region entries declared in the pax header. A malicious tar archive can therefore declare an extremely large number of sparse regions such that, when a Go program processes the archive (especially when reading from a compressed source), the program attempts to allocate a very large amount of memory based on those declared regions.
The immediate technical effect is predictable:

• A small crafted input can expand into extremely large memory allocations during parsing.
• An application processing the archive can hit out-of-memory conditions, trigger OOM-killer activity on Linux, or crash the process.
• Where the tar processing occurs inside long-running services, daemons, or automated pipeline components, a single crafted archive can cause widespread service disruption.

This is a classic resource-exhaustion (denial-of-service) vector enabled by missing limits during parsing of untrusted input. The underlying cause is not a buffer overflow or arbitrary code execution; it is excessive allocation and the availability of memory resources to be consumed by a single parsing operation.

Overview of current vendor response and Microsoft’s position​

Microsoft’s public messaging regarding this CVE states that the company has published machine-readable attestations (CSAF/VEX) starting with the Azure Linux Distribution, and that Azure Linux is the product for which Microsoft has published the vulnerability status. Microsoft also clearly said that if impact to additional products is identified, it will update the CVE attestation and related guidance.
Put plainly:

• Microsoft has published a VEX/CSAF attestation that covers the Azure Linux Distribution as part of its transparency initiative.
• Microsoft has not yet published VEX attestations or confirmed affected status for other Microsoft-branded products in that same channel for this CVE.
• Microsoft’s statement is an attestation of what they have validated so far, not a guarantee that no other Microsoft product includes an affected Go runtime or compiled artifact.

This is an important distinction: the published attestation documents the company’s current, validated exposure for that specific product. It does not, by itself, prove that other Microsoft software packages or services are not built with Go toolchains that include the vulnerable archive/tar code.

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Technical deep dive: who and what is affected​

Which code is vulnerable​

• The vulnerability is rooted in the Go standard library package archive/tar, specifically in logic that reads GNU pax 1.0 sparse map entries.
• Vulnerable code paths are those that parse pax-style sparse map headers and then allocate memory based on the declared number or size of regions.
• The issue affects Go versions prior to the patched releases; the maintainers published remediation releases in the 1.24.x and 1.25.x series (security patch releases contain the fix).

Typical places the library appears in real systems​

• Any software written and compiled in Go that uses the standard library’s archive/tar reader APIs is potentially vulnerable if built with an affected Go version.
• Common categories that frequently use Go and thus may indirectly be exposed:
• Container tooling and orchestration: many container engines, image-processing tools, builders, and utilities are written in Go or bundle Go-built binaries.
• CI/CD runners and image-build tooling that unpack tar archives or container layers.
• Cloud agents and control-plane components (some cloud-native services and internal tooling are implemented in Go).
• Third-party tooling distributed as compiled Go binaries embedded in other products.
• The presence of the Go runtime or Go-built binaries inside a product is the relevant indicator; inclusion in an OS distribution package (e.g., the golang toolchain) is a separate vector from compiled, statically-linked Go binaries.

What this means for Microsoft products broadly​

• Microsoft’s published attestation names the Azure Linux Distribution (the Azure Linux image family) as a product where Microsoft has validated the relevant package state and published a machine-readable status.
• That attestation should be read as Microsoft saying: “We have completed an inventory and published our official position for that particular product.” It is not an exhaustive inventory of all Microsoft-produced images, services, or binaries.
• Many Microsoft products and services run code or components that may have been built with Go toolchains at various points in their history. Determining whether a given Microsoft product includes a vulnerable archive/tar instance requires component-level inspection of that product’s build/toolchain or its run-time environment — i.e., it is not possible to infer a universal “no” or “yes” without that inventory.

Because of that uncertainty, organizations should treat the published Azure Linux attestation as an authoritative statement for that distribution while maintaining vigilance for any additional Microsoft products or third-party images they use that may contain Go-built artifacts.

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Cross-verified facts and what we confirmed​

• The vulnerability is tracked as CVE-2025-58183 and affects the Go standard library package archive/tar. The core defect is missing upper limits on the number of sparse region blocks in GNU pax 1.0 sparse files.
• The fix appears in Go security patch releases in the 1.24.x and 1.25.x lines; users are advised to upgrade to patched releases rather than relying on unpatched toolchains.
• Multiple independent vulnerability databases and maintainers of Linux distributions have cataloged the issue and issued updates or advisories to package maintainers and downstream consumers.
• Microsoft has publicly published a VEX/CSAF attestation covering the Azure Linux Distribution and has stated it will update the CVE if other product impacts are discovered.

Note: some claims about which individual Microsoft services or internal components might include vulnerable versions of Go cannot be independently verified from public data. Determining that requires internal build and deployment inventories that only Microsoft (or vendors who ship those binaries) can authoritatively disclose.

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Risk assessment for enterprises running Microsoft and third-party software​

Immediate risk profile​

• Likelihood of exploitation: moderate for environments where untrusted tar inputs are consumed by Go-based code. In many environments, tar archives are exchanged and processed automatically (CI pipelines, image registries, backup and restore tools). If a vulnerable Go-based consumer is present, the risk is non-trivial.
• Impact if exploited: denial-of-service (service crash or host memory exhaustion). In multi-tenant or shared-host contexts, a single crafted archive could affect co-located services.
• Remote exploitation: this depends on whether an attacker can provide a crafted tar archive to the vulnerable parser (e.g., via an upload API, unattended extraction process, or processing of user-supplied packages). In those cases, the attacker only needs to trigger parsing to cause resource exhaustion.

Specific concern areas for Microsoft customers​

• Azure customers running custom VMs or container workloads built with older Go toolchains: they should confirm whether their images include Go-based binaries built with vulnerable versions.
• Customers relying on Azure Marketplace images or third-party software that may include prebuilt Go binaries should verify those images’ SBOMs or vendor attestations.
• Organizations that rely on managed Microsoft services are partially insulated where Microsoft applies patches server-side; however, where customer-controlled agents or images are involved (e.g., Azure VM images, containers, or Marketplace appliances), the customer’s responsibility for updating remains.

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Practical detection, mitigation, and remediation steps​

The following actions are prioritized for security teams, platform engineers, and developers. They apply whether you run Microsoft-provided images, third-party images, or your own workloads.

1. Inventory and discovery (first and fastest step)​

• Produce a list of images, packages, and binaries that might contain Go runtimes or be compiled with Go.
• Use SBOMs, package managers, and container scanners to find occurrences of vuln-prone Go versions and the archive/tar package:
• Look for go toolchain packages (golang, go1.24, go1.25, etc. in OS repositories.
• Scan container images for compiled Go binaries and infer the toolchain version if available.
• Prioritize scanning of:
• Image-build pipelines and CI runners.
• Agents and daemons that process user-supplied tar archives or container layers.
• Marketplace images and VM images deployed across your estate.

2. Confirm whether binaries are built with vulnerable Go versions​

• Rebuild-time evidence: inspect the build pipelines and toolchain dependencies. If your binaries were compiled with an older Go toolchain (earlier than the patched releases), they are likely vulnerable.
• Run-time evidence: for some Go binaries, symbol strings or embedded version metadata can be inspected to infer the Go version used to compile them. Where unknown, assume risk and plan rebuilds.
• Container images: check the base image and build-time Dockerfile for “go” toolchain versions or run image scanners that extract build metadata.

3. Apply fixes and patches​

• For distributions and systems that package the Go toolchain, update to the vendor-supplied patched package versions.
• For compiled Go binaries under your control, rebuild them with patched Go releases (the security patches were released in the 1.24.x and 1.25.x lines).
• For third-party binaries or artifacts:
• Request rebuilds from the vendor or obtain patched releases.
• Replace with vendor-updated images or binaries where available.

4. Short-term mitigations if immediate rebuilds are not possible​

• Introduce operational controls to limit exposure:
• Block or sandbox processing of untrusted tar inputs in highly-privileged services.
• Rate-limit or queue archive processing and monitor memory use.
• Run tar-parsing operations in isolated containers with strict memory limits and OOM behaviors controlled so they do not affect other services.
• Deploy content scanning and pre-validation for archives before they reach vulnerable parsers:
• Inspect pax headers for suspiciously large sparse-map declarations.
• Reject archives with metadata inconsistent with expected sizes.
• Apply host-level memory limits (cgroups) or set container memory limits to avoid host-wide OOM events.

5. Monitoring and detection​

• Watch for spikes in memory usage, OOM kills, or repeated crashes in processes that handle tar archives.
• Alert on logs that show tar extraction failures or unexpected resource exhaustion.
• Forensics: capture samples of suspicious tar archives for analysis; instrument parsing code to log suspicious pax headers before allocation.

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Developer recommendations: harden code that uses archive/tar​

• Do not trust archive metadata. Apply maximum sanity checks before using header fields to drive allocations.
• For high-risk inputs, wrap tar reading in safe guards, for example:
• Pre-validate the pax header entry count and reject values exceeding an application-defined threshold.
• Use incremental parsing and allocate only after cumulative sanity checks rather than trusting a single metadata field.
• Consider defensive patterns such as using io.LimitedReader or custom readers that cap total bytes processed when reading compressed streams.
• Test parsers with fuzzing and large-but-compressed test payloads to ensure compression-amplification attacks are detected.

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Why Microsoft’s attestation for Azure Linux does not equal “only product” — and what that means​

Microsoft’s published CSAF/VEX attestation for the Azure Linux Distribution is a transparency milestone: the company has supplied machine-readable status for that distro. However:

• The presence of a VEX/CSAF attestation for one product does not imply that other Microsoft products do not include the vulnerable library.
• An exhaustive list of affected Microsoft products would require per-product inventory and validation; Microsoft’s process is iterative and they have publicly committed to updating the CVE status if additional impacts are found.
• Independent verification of Microsoft’s internal build toolchains or compiled artifacts for all Microsoft products is not possible from outside the company. Therefore, customers must treat Microsoft’s current attestation as authoritative for the Azure Linux Distribution and must also proactively inventory their own deployed software, including third-party content and custom-built Go binaries.

This is a standard industry reality in supply-chain vulnerabilities: vendor attestations are necessary and valuable, but they do not replace customer-side inventory and validation.

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Recommended checklist for Windows and Azure administrators (actionable, prioritized)​

• Immediately confirm whether any of your customer-controlled images or agent binaries are Go-built and compiled with an affected toolchain.
• Patch Azure Linux VMs and images where Microsoft publishes fixes for that distribution.
• For any self-hosted or third-party Go binaries, rebuild or update them to use patched Go releases.
• Apply container memory limits and sandboxing for tar-processing services as a temporary mitigation.
• Enable monitoring that alerts on process OOM and high-memory events in services that handle archive inputs.
• Update CI/CD pipelines to pin and use patched Go toolchain versions; recompile artifacts and redeploy.
• Subscribe to official vendor attestation feeds and CSAF/VEX updates for automated ingestion into vulnerability management tools.

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Broader implications for supply-chain security and vendor transparency​

This vulnerability reinforces several supply-chain lessons that are now familiar but still critical:

• Machine-readable attestations (CSAF/VEX) are useful, but they are only as effective as the breadth and cadence of vendor inventory efforts.
• Customers must combine vendor attestations with internal SBOM generation, image scanning, and runtime detection to assert their true exposure.
• The nature of modern binaries — statically-linked Go executables, containerized workloads, and third-party images — means that vulnerabilities in a language runtime can show up anywhere in the stack.
• Clear vendor statements that they will update attestations if more products are affected are valuable, but they require ongoing monitoring from customers until the vendor’s entire product surface has been validated.

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Final assessment and guidance​

• Microsoft’s current public attestation confirms that the Azure Linux Distribution has been validated and included in their machine-readable CSAF/VEX disclosures. That is a positive, transparent step that helps customers automate risk decisions for that specific product.
• However, the attestation does not and cannot, by itself, guarantee that other Microsoft products are unaffected. The only authoritative way to confirm exposure for other Microsoft-branded products is either a vendor attestation for those products or an independent inventory of the artifacts in use.
• For organizations: assume the risk model that any Go-built component you operate could be exposed until you confirm otherwise. Prioritize inventory, rebuilds with patched Go toolchains, and sandboxing of tar-processing workloads.

Takeaway: treat Microsoft’s Azure Linux attestation as official and actionable for that distribution — and treat the remainder of your estate as requiring immediate inventory and, where relevant, urgent rebuilds or mitigations. Vigilant scanning, vendor tracking, and rapid application of patched builds are the practical defenses that will reduce the blast radius of CVE-2025-58183.

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Source: MSRC Security Update Guide - Microsoft Security Response Center