T08 · Insecure Dependencies
- Location
SKILL.md:289- Finding
Unpinned Third-Party Package Download and Execution
- Content
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Vulnerability Details
File Location:
SKILL.md, lines 289–294
Vulnerability Type: Unpinned npm dependency executed throughnpx
Risk Level: MediumComplete Code Snippet
bash ### Third step: Validate standards compliance # Check with the W3C validator # Visit validator.w3.org and paste the HTML code # Or use a command-line tool npx html-validator-cli --file index.htmlThe headings and comments above are English translations of the original documentation; the executable command is reproduced verbatim.
Technical Analysis
The documented command invokes
html-validator-clithroughnpxwithout specifying a reviewed version. If the package is not already available locally,npxmay retrieve it from the configured npm registry and immediately execute its code.The project does not provide a package manifest, lockfile, integrity metadata, publisher verification, or other mechanism that binds this command to an audited package artifact. Consequently, the code executed later can differ from the code available when the Skill was reviewed. Relevant supply-chain scenarios include compromise of the legitimate package or publisher account, publication of a malicious or unexpectedly changed release, and substitution through a compromised or attacker-controlled registry configuration.
This is especially relevant because the Skill declares
execcapability in its metadata. The command is presented as a normal validation step, making execution by an Agent or user reasonably foreseeable.Attack Path
- An attacker compromises the package, its publisher account, or the npm registry path used by the environment and publishes a malicious release under
html-validator-cli. - A user asks the Skill to validate an HTML file.
- The Agent or user follows the documented
npx html-validator-cli --file index.htmlcommand. npxresolves and downloads the mutable, unpinned package release.- P ...[truncated 1093 chars]
- An attacker compromises the package, its publisher account, or the npm registry path used by the environment and publishes a malicious release under
- Remediation
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Remediation Suggestions
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Pin the command to a specifically reviewed package version, for example:
bash npx --yes html-validator-cli@REVIEWED_VERSION --file index.htmlPinning alone does not provide complete integrity protection, but it prevents silently selecting a newer release.
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Prefer declaring the validator as a development dependency in
package.jsonand committing a lockfile containing registry URLs and integrity hashes:bash npm ci npm exec -- html-validator-cli --file index.html -
Review the package name, publisher, source repository, release provenance, dependency tree, and selected version before approving it.
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Where compatible with the package, suppress dependency lifecycle scripts during installation:
bash npm ci --ignore-scriptsTest this configuration because some legitimate packages require installation scripts.
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Configure npm to use an approved registry and enforce lockfile integrity in CI. Consider dependency allowlisting, provenance verification, and automated package-risk scanning.
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Run validation in a sandbox with least privilege, no unnecessary secrets, restricted filesystem mounts, and constrained outbound network access.
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Prefer a built-in, locally reviewed validator when available. If an online validation service is used instead, disclose that submitted HTML leaves the local environment and avoid transmitting confidential content.
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