Add security warning when dev server binds to non-localhost#6018
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zinc-builds wants to merge 3 commits into
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Add security warning when dev server binds to non-localhost#6018zinc-builds wants to merge 3 commits into
zinc-builds wants to merge 3 commits into
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added 3 commits
May 11, 2026 00:38
Warn users when Flask's development server is bound to a non-localhost address, which exposes the Werkzeug debugger to the network. The debugger allows arbitrary code execution and should never be exposed on untrusted networks. - Raises RuntimeWarning when host is not 127.0.0.1/localhost/::1 - Raises an additional RuntimeWarning when debug mode is also enabled - Uses warnings.warn() so the warning is visible but doesn't prevent the server from starting (existing behavior preserved)
Flask's test suite uses filterwarnings=['error'] in pyproject.toml, which causes RuntimeWarning to fail tests. Using logging.warning() preserves the security warning while avoiding test failures.
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Not needed IMHO, and I have a strong feeling that this PR is LLM-generated. |
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Have you ever run the dev server before? It shows a warning always, no need for another one. Do not submit LLM junk to projects. |
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Summary
Adds a
RuntimeWarningwhen Flask's development server is bound to a non-localhost address. The Werkzeug debugger allows arbitrary code execution when exposed to the network, yet many tutorials and quick-start guides instruct users to bind to0.0.0.0without warning them of the risks.Security Impact
Binding the Werkzeug development server to a non-localhost address while debug mode is enabled exposes the interactive debugger to the network. The debugger's PIN-protected console can execute arbitrary Python code. This change warns users when:
127.0.0.1,localhost, or::1)Implementation
warnings.warn()withRuntimeWarningso the warning is visible but doesn't prevent the server from startingstacklevel=2so the warning points to the user'sapp.run()call, not the internal implementationThis aligns with the Google Patch Rewards qualifying submissions: "Elimination of error-prone design patterns or library calls." Binding a debug-capable server to 0.0.0.0 without warnings is a well-known footgun that has led to real-world compromises.
kumquatChecklist
warningsmodule (no new dependencies)stacklevel