tiktoken-mcpPyPI
Malicious code in tiktoken-mcp (PyPI) Remove it immediately and rotate any exposed credentials.
What this malware does
tiktoken-mcp impersonates the OpenAI-published tiktoken package: its METADATA copies the upstream Name/Summary, Author 'Shantanu Jain', Author-email '[email protected]', and Project-URL pointing at github.com/openai/tiktoken, with the upstream README bundled. The package ships tiktoken-setup.pth, which Python's site.py auto-executes at every interpreter start. The.pth contains an obfuscated exec() blob (single-letter underscore-prefixed aliases for os/subprocess/urllib.request/platform/sys/shutil/glob) that, on first run, downloads the Bun JS runtime from https://github.com/oven-sh/bun/releases/download/bun-v1.3.13/bun-<platform>-<arch>.zip, extracts it to /tmp/b/bun, then walks sys.path searching for any file named '_index.js' in any package directory and executes it with 'bun run'. The package itself does not ship an _index.js, so the bytes ultimately executed are whatever a co-installed package places on sys.path under that name — i.e., attacker-controlled, runtime-resolved content executed via a non-Python runtime that bypasses Python-only inspection. The package's stated purpose is BPE tokenisation; there is no advertised reason for a JS runtime. This is an alternate-runtime dropper combined with brand impersonation of a top-tier OpenAI package.
Typosquatting package published from a compromised account with an embedded infostealer. The infostealer is a heavily obfuscated JavaScript code executed using Bun runtime on Python startup. It collects all kinds of sensitive data, including API keys, credentials to package repositories, cryptocurrency assets, password manager data. Infostealer actively queries online services to collect additional secrets as well as attempts to gain persistence and spread further by publishing infected packages using collected credentials. Data are exfiltrated likely using Github. The code seems to threaten to wipe the user's data if it detects invalid GitHub tokens. Cleanup should be done with caution.
It seems to be related to the recent Mini Shai Hulud campaign.
Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.
Campaign: 2026-06-compr-woodpecker
Reasons (based on the campaign):
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compromised-package
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exfiltration-env-variables
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exfiltration-cloud-tokens
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exfiltration-credentials
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abuses-pth
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obfuscation
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infostealer
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The package contains code to detect if it is running in a sandbox environment.
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exfiltration-crypto
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files-exfiltration
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destructive-actions
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for tiktoken-mcp (2 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging tiktoken-mcp across your stack and pipelines.
If you installed it — respond
tiktoken-mcp is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.
Did it already run?
If tiktoken-mcp was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks tiktoken-mcp before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
- Kamil Mańkowski (kam193) · analyst
Detect & block this
O3 blocks tiktoken-mcp-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.