Microsoft’s GitHub repositories taken offline amid Miasma supply chain attack
Miasma, a self-replicating malware strain, has evolved from the Mini Shai-Hulud worm
GitHub, which is owned by Microsoft, has disabled access to at least 73 repositories across four Microsoft organisations after they were compromised in what security researchers describe as one of the most aggressive software supply chain attacks seen to date.
Affected repositories span several key Microsoft projects, including Azure services, developer tools and technical documentation.
Users attempting to access some repositories are now greeted with a notice stating that access has been disabled.
"Access to this repository has been disabled by GitHub Staff due to a violation of GitHub's terms of service," reads the message.
Among the impacted projects are components of Microsoft's Durable Task ecosystem and developer connectors.
Researchers at OpenSourceMalware said the incident appears to be linked to Miasma, a self-replicating malware strain that has evolved from the Mini Shai-Hulud worm, whose source code was publicly released by the TeamPCP threat group in May.
Experts describe the latest attack as a "re-compromise" of the Durable Task software supply chain.
Security researcher Paul McCarty, known online as "6mile", said the widespread removal of repositories connected to the Durable Task project suggests attackers may have retained access obtained during an earlier breach.
"When the repo at the root of last month's compromise is the hub of this month's takedown, that is not a coincidence - that is the same wound reopening. Whoever held those credentials in May plausibly never fully lost them," he said.
How Miasma spreads
Researchers say Miasma spreads by stealing developer credentials, cloud secrets, SSH keys and software deployment tokens.
Once access is obtained, attackers can modify legitimate software packages and repositories, allowing malware to spread through trusted updates.
Security company SafeDep said that recent versions of the campaign bypassed traditional package registries altogether. Instead, attackers allegedly inserted malicious code directly into popular GitHub repositories, including several projects associated with the Mantine open-source ecosystem.
The malicious additions installed a large payload designed to activate automatically through widely used developer tools and AI-assisted coding environments, including Claude Code, Gemini CLI, Cursor and Visual Studio Code.
Variants of Shai-Hulud-based malware
Over recent months, variants of Shai-Hulud-based malware (named after the sandworm in the sci-fi epic Dune) have been linked to attacks affecting a number of prominent technology projects and organisations, including Bitwarden, Mistral, SAP, TanStack, OpenAI and GitHub.
Last month, cybersecurity firms Aikido and OX Security uncovered another Miasma-related campaign involving more than 30 compromised software packages associated with Red Hat's cloud services ecosystem.
The affected packages were estimated to receive more than 117,000 downloads each week.
Experts warn that the campaign demonstrates a fundamental weakness in modern software development, which relies heavily on trust between maintainers, package registries and downstream users.
"The worm's genius and the reason conventional defences largely failed is that it operates entirely within legitimate channels. It does not exploit a vulnerability in npm or GitHub," researchers at FalconFeeds.io said.
Rather than exploiting flaws in platforms such as GitHub or npm, the malware targets trusted developer accounts and signing credentials.
Because malicious updates are published using legitimate authentication methods, they can appear indistinguishable from routine software releases, the researchers noted.