Critical Microsoft Vulnerability: 73 Packages Deploy Password Stealers

Key Takeaways

• Microsoft disabled 73 GitHub repositories on June 8, 2026, following a widespread compromise by the Miasma worm.
• The self-replicating malware, also known as “The Spring Blight,” infiltrated Microsoft’s Azure Functions ecosystem by injecting malicious versions of the durabletask PyPI package.
• The worm stole GitHub Actions secrets, Azure OIDC authentication hashes, and managed-identity tokens, exfiltrating them to an external service called TempGPT.
• The incident highlights significant supply chain vulnerabilities within Microsoft’s developer infrastructure, affecting critical Azure and GitHub organizations.

Worm Infiltrates Azure Functions, Prompts Rapid GitHub Shutdown

On June 8, 2026, Microsoft initiated a rapid response, deactivating 73 of its GitHub repositories in a span of just 105 seconds. This decisive action, occurring between 19:00 and 19:02 UTC, was a direct consequence of a sophisticated, self-replicating worm that had deeply penetrated the company’s Azure Functions ecosystem. What initially appeared as a standard enforcement measure was, in fact, the culmination of a covert intrusion campaign that had been underway for several months.

The malware responsible for this compromise is identified as Miasma, or alternatively, “The Spring Blight.” This worm operates by spreading across GitHub repositories, exploiting supply-chain packages to steal developer credentials and then replicating itself into new projects. Its reach extended to four of Microsoft’s primary GitHub organizations: Azure, Azure-Samples, microsoft, and MicrosoftDocs, impacting repositories that are integral to millions of developers globally.

Analysts at OpenSource Malware detailed the intrusion in a report shared with Cyber SecurityNews (CSN). Their investigation linked the June 8 incident to a broader campaign utilizing the Shai-Hulud toolkit, which had previously targeted AWS and GitHub environments. In this latest iteration, attackers specifically escalated their efforts to acquire Azure credentials.

The incident also triggered widespread disruptions for developers. The disabling of Azure/functions-action by GitHub led to an immediate failure of all CI/CD pipelines that referenced Azure/functions-action@v1. Microsoft initially characterized the event as an “internal management issue,” but revised this explanation within twelve minutes as the full scope of the compromise became evident.

The extensive nature of the breach has raised concerns about the integrity of Microsoft’s own supply chain. The presence of a credential-harvesting worm at the heart of the Azure Functions ecosystem is a serious event, and the speed of its propagation underscored the meticulous planning behind the attack.

73 Microsoft Packages Weaponized by Miasma

Miasma gained its initial foothold through the durabletask PyPI package, a critical component of Microsoft’s Durable Task framework, which is widely used across Node.js, Python, Java, Go, JavaScript, MSSQL, Netherite, and protobuf implementations. Attackers uploaded three malicious versions—1.5.1, 1.5.2, and 1.5.3—to PyPI within a 38-minute window. These uploads lacked corresponding tags, releases, or CI runs in the GitHub repository, serving as a significant indicator of malicious activity.

Before detection, these compromised versions accumulated approximately 31,000 downloads. The malicious packages incorporated preinstall hooks that executed Bun against a non-robust index.js loader, now recognized as Miasma’s signature execution method. Once embedded within a developer’s environment, the worm proceeded to steal GitHub Actions secrets, exfiltrating them to an external service named TempGPT.

Beyond GitHub credentials, Miasma specifically targeted Azure OIDC authentication hashes and managed-identity tokens. These tokens are crucial for cloud applications to authenticate with Azure services without storing passwords, making their theft particularly dangerous as it grants attackers stealthy, persistent access to cloud infrastructure that is difficult to detect and revoke.

Credential Theft and Worm-Like Propagation Across Azure

Upon harvesting credentials, Miasma continued its malicious activities by creating public GitHub repositories within the victim’s accounts. These repositories were labeled “Miasma: The Spring Blight” and contained the stolen secrets committed as JSON files. This surge of repository creation activity ultimately triggered GitHub’s automated terms-of-service enforcement, leading to the rapid shutdown of 73 repositories.

Previous variants of the Shai-Hulud toolkit had concentrated on AWS access keys and GitHub personal tokens. This latest iteration, however, broadened its attack surface to include Azure OIDC and managed-identity layers, signifying a notable escalation in both scope and ambition.

What You Should Do

• Pin Actions to Full Commit SHAs: For Azure Functions pipelines, security researchers strongly advise pinning actions to a full commit SHA rather than relying on floating tags like @v1.
• Rotate Credentials: Prioritize rotating Azure OIDC tokens, managed-identity credentials, and any npm or PyPI tokens accessible from affected workflows.
• Audit Package Install Hooks: Inspect package install hooks for any preinstall scripts that invoke Bun against unfamiliar index.js loaders.
• Utilize Microsoft’s Alternatives: Until Azure/functions-action is fully restored, Microsoft recommends using alternatives such as Azure CLI, Azure DevOps Pipelines, VS Code deployment, and Zip Deploy.
• Check GitHub Organizations: Organizations that utilized the compromised repositories should audit their GitHub organizations for any unexplained public repositories referencing “The Spring Blight” campaign.

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