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+# Diagnosis: Bun response headers leaked via transaction context (Set-Cookie exfiltration)
+
+Issue: https://github.com/getsentry/sentry-javascript/issues/19790
+
+## Root cause hypotheses
+1. During Bun integration, response headers are being serialized into performance telemetry and attached to transaction payloads.
+2. `getCapturedScopesOnSpan` stores data into `isolationScope` and this scope is merged into transaction context, potentially including headers.
+3. The Bun HTTP transport or instrumentation may be attaching full `Response` headers (including `Set-Cookie`) to span/transaction metadata.
+
+## Files likely needing modification
+- `packages/bun/src/integrations/http.ts` (or equivalent Bun instrumentation file)
+- `packages/core/src/tracing/transaction.ts`
+- `packages/core/src/span.ts` (or where telemetry payloads are built)
+- Any utility serializing headers to telemetry (e.g., `packages/utils/src/header.ts`)
+
+## Verification steps
+1. Reproduce by starting a Bun server with Sentry SDK and inspecting transaction payloads for presence of `response.headers` or `Set-Cookie`.
+2. Add a debug logger before telemetry serialization to dump keys/values being attached to spans.
+3. Confirm that removing header serialization or redacting `Set-Cookie` prevents leakage.
+
+## Recommended minimal patch approach
+- Before including response headers in telemetry, redact or exclude sensitive headers (`Set-Cookie`, `Authorization`, etc.).
+- Ensure `getCapturedScopesOnSpan` does not merge raw response headers into scopes.
+
+## Next actions
+- Implement a redaction utility for response headers.
+- Modify Bun HTTP integration to use this utility before attaching headers to spans.
+- Add unit tests verifying no sensitive headers are present in captured telemetry.