Security: Logical ID uniqueness check can be bypassed via substring matching#3911
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The `verify_unique_logical_id` function uses the `in` operator to compare resource types against `do_not_verify` entries. For mappings where the value is a string (not a list), `in` performs substring checks, not strict equality. This can allow unintended type matches (e.g., crafted type strings that are substrings), potentially bypassing logical ID collision detection and causing transformed resources to overwrite or collide with existing ones. Affected files: verify_logical_id.py Signed-off-by: tuanaiseo <221258316+tuanaiseo@users.noreply.github.com>
reedham-aws
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Apr 17, 2026
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I disagree that this is a security related fix, but I guess it's a good enough defensive programming adjustment.
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Problem
The
verify_unique_logical_idfunction uses theinoperator to compare resource types againstdo_not_verifyentries. For mappings where the value is a string (not a list),inperforms substring checks, not strict equality. This can allow unintended type matches (e.g., crafted type strings that are substrings), potentially bypassing logical ID collision detection and causing transformed resources to overwrite or collide with existing ones.Severity:
mediumFile:
samtranslator/translator/verify_logical_id.pySolution
Use strict type comparison. Normalize
do_not_verifyvalues to lists and compare with equality, e.g.allowed = do_not_verify[resource.resource_type]; allowed_types = allowed if isinstance(allowed, list) else [allowed]; return existing_type in allowed_types.Changes
samtranslator/translator/verify_logical_id.py(modified)Testing