fix: mitigate timing-based user enumeration in password grant - #2693
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Mahaveer1013 wants to merge 2 commits into
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fix: mitigate timing-based user enumeration in password grant#2693Mahaveer1013 wants to merge 2 commits into
Mahaveer1013 wants to merge 2 commits into
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ResourceOwnerPasswordGrant only ran a bcrypt comparison when a user was found and had a password set. The not-found and no-password branches returned immediately, making response time distinguishable from a real failed-password attempt (~75-80ms gap at default bcrypt cost), which discloses account existence. Generate a fixed decoy hash at startup (same cost as real password hashes) and compare against it on both short-circuit branches before returning the same invalid_credentials error, so timing no longer depends on whether the account exists. Closes supabase#2674 Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Summary
ResourceOwnerPasswordGrantonly performed a bcrypt comparison when thelooked-up user existed and had a password set. The not-found and
no-password branches returned the
invalid_credentialserror immediately,with no comparable work — making response time distinguishable from a real
failed-password attempt (~75-80ms gap at default bcrypt cost measured
against a hosted project) and disclosing whether an account exists.
bcrypt cost used for real user passwords (
crypto.GenerateFromPassword,same call site pattern as
internal/models/user.go).compareDummyPasswordHash, which runs a bcrypt compare against thatdecoy hash and swallows the expected mismatch error.
ResourceOwnerPasswordGrant(user not found, and user found but has no password) before returning
the same
invalid_credentialserror, so timing no longer depends onwhich branch was taken.
No change to response status codes, error codes, or response bodies —
this only equalizes latency.
Closes #2674
Test plan
go build ./...gofmt -lclean on changed filesgo vet ./internal/api/...go test ./internal/api/... -run TestToken -v -count=1— all password grant tests pass, including newTestTokenPasswordGrantMissingUserChecksDummyPasswordHash, which corrupts the decoy hash and asserts the not-found branch now surfaces the comparison failure (500), proving the helper is actually wired into that branch.