Stop MIME scanner probes from creating Rollbar noise - #2881
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Rails has mapped ActionDispatch::Http::MimeNegotiation::InvalidType to :not_acceptable in rescue_responses since Rails 6.1, so malformed Accept/Content-Type headers already get 406 responses. Rollbar still reported the handled exception because its middleware reports anything passing through. Add the exception class to exception_level_filters as "ignore", the same treatment RoutingError already receives.
Return 406 from nginx when the Accept or Content-Type header contains a path-traversal pattern, keeping these probes out of the application access logs entirely.
mroderick
marked this pull request as ready for review
September 16, 2026 10:38
KimberleyCook
approved these changes
Sep 16, 2026
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Fixes #2873
Corrected diagnosis
The issue description assumed these probes cause 500s and that
rescue_responsesneeds the mapping added. Neither holds on Rails 8.1.3.1:ActionDispatch::Http::MimeNegotiation::InvalidTypehas been mapped to:not_acceptablein the defaultrescue_responsessince Rails 6.1 (rails/rails commit 2bad7eb1, 2020). Malformed Accept/Content-Type headers already get 406 responses.RollbarMiddlewarereports every exception passing through it (:use_exception_level_filters => true), even ones Rails has already rescued and rendered as 406.Verification of the middleware chain
config/initializers/rollbar.rbalready ignoresActionController::RoutingErrorviaconfig.exception_level_filtersfor the same reason. Rollbar'sExceptionReporter#exception_datapassesuse_exception_level_filters: true, and'ignore'values suppress reporting entirely (rollbar 3.8.0,lib/rollbar/notifier.rb).Changes
config/initializers/rollbar.rb) — addActionDispatch::Http::MimeNegotiation::InvalidTypetoexception_level_filtersas'ignore'. This stops the Rollbar noise regardless of which header shape the bots use.config/nginx.conf.erb) — amapon the combined Accept/Content-Type headers returns 406 when either contains../, keeping these probes out of the application's access logs.Testing
spec/config/rollbar_config_spec.rbasserts the filter is registered (written first, failed withnilbefore the initializer change).spec/requests/malformed_mime_headers_spec.rbcharacterises the existing 406 behaviour for both headers.bundle exec parallel_rspec spec/ -n 3— 1446 examples, 0 failures. RuboCop clean on changed files.curl -s -o /dev/null -w '%{http_code}' -H 'Accept: ../../etc/services{{' https://<staging-host>/should return 406.