fix(bb-file-bucket): harden dev file server against stored XSS and token forgery - #292
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…ken forgery The local dev file server served attacker-controlled bodies inline under an attacker-controlled Content-Type (stored-XSS primitive), and signed presigned-URL tokens with a hardcoded, source-visible secret (forgeable offline). - GET responses now send X-Content-Type-Options: nosniff and Content-Disposition: attachment so an uploaded text/html/SVG payload can't execute in the app origin. - LOCAL_FILE_SECRET is now a per-process random value instead of a fixed literal. The token-minting mock and the validating dev server share one in-process module instance, so local presigned-URL round-trips still work. Adds regression tests (both verified red on the old code): nosniff+attachment on GET, and rejection of a token forged with the former hardcoded secret.
🦋 Changeset detectedLatest commit: f7c59c8 The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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soberm
approved these changes
Aug 4, 2026
Simone319
approved these changes
Aug 5, 2026
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What
Harden the local dev file server (
packages/bb-file-bucket/src/file-server.ts) against two issues in the same code path:Content-Type. Any client with a presigned PUT can upload atext/html/SVG payload; served inline it executes in the local app's origin. Now every download sends:X-Content-Type-Options: nosniffContent-Disposition: attachment'__blocks_file_bucket_dev_secret__'), so anyone could mint a valid token offline for anyfullId/path/method without ever callinggetUrl()/putUrl().LOCAL_FILE_SECRETis now a per-process random value (randomBytes(32)). The token-minting mock (index.mock.ts) and the validating dev server (file-server.ts) import the same in-process module instance, so local round-trips are unaffected; only offline forgery is closed.LOCAL_FILE_SECRETandtokens.tsare internal (not in the packageexportsmap, not inAPI.md), so this is not a public API change.Why
Board bug-bash card (P0 / Security): bb-file-bucket: dev mock signs uploads with hardcoded secret + serves text/html — https://github.com/orgs/aws-amplify/projects/141/views/15?pane=issue&itemId=195528277
Keeps local dev no weaker than an S3 object served behind CloudFront.
Testing
Two regression tests added to
file-server.test.ts, both verified red on the old code, green with the fix:GET sends
nosniff+Content-Disposition: attachmentafter uploading an HTML payload.A token forged with the former hardcoded secret is rejected (403).
npm run build(full monorepo) — passesnpm testinpackages/bb-file-bucket— 92 tests, 0 failuresbiome lint --changed --since=origin/main— cleanDESIGN.mdupdated (token-secret + download-hardening notes)Changeset
Included (
@aws-blocks/bb-file-bucketpatch).Scope note
The card mentions the mock also "serves whatever was uploaded as text/html". This PR addresses that via response hardening (nosniff + attachment) rather than rewriting content-type handling, and closes the hardcoded-secret half. Both halves of the card are covered.