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Potentially sensitive data should not be used in the ARG or ENV commands.
PropertyValue
SeverityWarning
CategorySecurity
DefaultEnabled

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Description

While it is common to pass secrets to running processes through environment variables during local development, setting secrets in a Dockerfile using ENV or ARG is insecure because they persist in the final image. This rule reports violations where ENV and ARG keys indicate that they contain sensitive data. Instead of ARG or ENV, you should use secret mounts, which expose secrets to your builds in a secure manner and do not persist in the final image or its metadata.

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Examples

Bad: 
FROM scratch
ARG AWS_SECRET_ACCESS_KEY
Good (use secret mounts instead): 
FROM scratch
RUN --mount=type=secret,id=aws_key \
    AWS_SECRET_ACCESS_KEY=$(cat /run/secrets/aws_key) \
    aws s3 cp ...
See also: tally/secrets-in-code complements this rule by detecting actual secret values (not just variable names).

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Reference