fix(no-ticket): stricter acceptance of api hosts and proxies

[cloudsmith-iduffy]

Description

Directory-relative config files (config.ini is searched in the current working directory first) can set api_host / api_proxy to an arbitrary endpoint. Because credentials are attached to whatever host/proxy is configured, a malicious repository shipping a ./config.ini could cause the next cloudsmith command run inside it to leak the user's API key or bearer token to an attacker-controlled endpoint.

This change enforces an allow-list only on untrusted (directory-relative) sources:

• When the effective api_host originates from a cwd config and was not supplied via --api-host / CLOUDSMITH_API_HOST, it must be under *.cloudsmith.io or *.cloudsmith.com.
• Any api_proxy originating from such a source is rejected outright (there is no sensible domain allow-list for proxies).
• Trusted sources — CLI flags, environment variables, user/home config, and an explicit --config-file — are unaffected, preserving dedicated/on-prem deployments that use custom hosts.

Hostname matching parses the URL netloc (defending …cloudsmith.io.evil.com, …cloudsmith.io@evil.com, port/userinfo tricks). Additional trusted suffixes can be supplied via the hidden --allowed-api-host-suffixes option / CLOUDSMITH_ALLOWED_API_HOST_SUFFIXES env var — wired through Click only, never the config-file schema, so an untrusted config cannot whitelist its own domain.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactoring
• Other (please describe)

Additional Notes

Low blast radius: only a directory-relative config.ini setting a non-cloudsmith api_host or any api_proxy is affected — exactly the credential-redirection cases reported. Values from env vars, flags, and user/home config are untouched.

Follow-ups noted but intentionally out of scope: api_ssl_verify=false and api_headers from untrusted config are the same MITM class and could be guarded similarly.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Hardens the CLI against credential exfiltration via directory-local (./config.ini) configuration by restricting untrusted api_host values to Cloudsmith domains and disallowing untrusted api_proxy entirely, while keeping trusted sources (flags/env/home config/explicit --config-file) functional for dedicated/on-prem setups.

Changes:

• Added hostname extraction + suffix allow-list validation for api_host, plus unconditional rejection for untrusted api_proxy.
• Introduced a CLI-only (hidden) escape hatch for additional allowed host suffixes via --allowed-api-host-suffixes / CLOUDSMITH_ALLOWED_API_HOST_SUFFIXES.
• Added config-reader support for extracting values specifically from directory-relative config, plus a focused test suite.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
cloudsmith_cli/cli/validators.py	Adds hostname parsing and allow-list enforcement helpers for untrusted API endpoint settings.
cloudsmith_cli/cli/decorators.py	Wires enforcement into session initialization and adds hidden option/env var to extend trusted suffixes.
cloudsmith_cli/cli/config.py	Implements reading specific keys from directory-relative config and quote-stripping behavior.
cloudsmith_cli/cli/tests/test_api_host_validation.py	Adds unit tests covering hostname parsing, allow-list behavior, and enforcement gating logic.

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