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The S3 client builds its own request headers. The option-time check for contentDisposition, type and contentEncoding and the sign-time check for the session token, access key id, region, host and the other signed values rejected CR and LF only. A NUL byte reached the wire inside x-amz-security-token, Authorization, content-disposition and content-encoding. fetch() rejects NUL, CR and LF alike. Both checks now share one helper in bun_s3_signing that rejects the same byte set as fetch. The error paths are unchanged: the option check throws at call time, the sign-time check fails with ERR_S3_INVALID_SIGNATURE.
WalkthroughChangesS3 header validation
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Status Reproduced on bun 1.4.0 with a raw TCP stub as the endpoint. Fix: both S3 checks (option parsing and signing) now use one helper that rejects NUL, CR and LF. Tests: Waiting for CI. |
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LGTM — adds NUL to the existing CR/LF rejection set for S3 header-bearing values.
What was reviewed:
contains_any(value, b"\0\r\n")is a strict superset of the oldindex_of_any(value, b"\r\n").is_some(); valid inputs are unaffected.- The duplicated
contains_newline_or_crincredentials_jsc.rsis removed in favor of the sharedbun_s3_signinghelper; the now-unusedstringsimport is dropped;pub use credentials::*re-exports the new helper. - All three error-message call sites and the one exact-match assertion in
s3-fd-validation.test.tsare updated; the pre-existing/CR\/LF/regex assertions still match the new wording. - New tests use
port: 0,usingdisposal,test.eachover the option/credential matrix, buffer to\r\n\r\nframing in the raw TCP stub, and include a positive control.
Extended reasoning...
Overview
Two Rust source files and two test files. The functional change is a one-byte extension to an existing validation set: b"\r\n" → b"\0\r\n". The helper is renamed contains_newline_or_cr → contains_invalid_header_value_byte, made pub, and the duplicate copy in credentials_jsc.rs is deleted in favor of importing the one from bun_s3_signing (which glob-re-exports credentials::*). Three error messages are reworded to mention NUL. One existing test assertion is updated to match; the other pre-existing assertions use /CR\/LF/ which still matches. Six new tests cover NUL in contentDisposition/contentEncoding/type (synchronous throw) and sessionToken/accessKeyId/region (sign-time ERR_S3_INVALID_SIGNATURE), plus a positive control. The test file gains proxy-env blanking via beforeAll/afterAll, mirroring test/js/bun/http/proxy.test.ts.
Security risks
This is a hardening change. It only tightens validation — inputs without NUL are unaffected because strings::contains_any is exactly index_of_any(...).is_some() and the new needle set is a superset. The rejected byte set (NUL, CR, LF) matches the Fetch spec's header-value rule as noted in the doc comment. No new user-controlled data reaches a header; the change stops one more byte class from reaching it. No auth, crypto, or permission logic changes.
Level of scrutiny
Low-to-medium. The core change is a mechanical extension of an existing check along an already-tested code path (CR/LF was covered by the same tests file). No new control flow, no allocation or lifetime changes, no error-path restructuring. The de-duplication of the helper is a straight code-quality improvement encouraged by the review guidelines.
Other factors
Test coverage is thorough: test.each over both option and credential matrices, a raw Bun.listen stub (with a comment explaining why Bun.serve can't observe the failure mode), buffering to the HTTP header terminator before asserting, using for cleanup, describe.concurrent, and a positive control confirming clean credentials still reach the wire. The PR description shows fail-before output on 1.4.0 for all six new tests. I grepped for the old error message wording and found no remaining references. No prior human reviews or outstanding comments on the PR.
The second test in this file uploads to a local Bun.serve. With an ambient HTTP_PROXY the S3 client sends that upload to the proxy instead, so the file failed in environments that set one. Same approach as s3-header-injection.test.ts and test/js/bun/http/proxy.test.ts.
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Actionable comments posted: 2
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Inline comments:
In `@src/s3_signing/credentials.rs`:
- Around line 811-823: Move the invalid-value validation in the sign_query flow
before its early return, ensuring access_key_id, region, session_token, and the
other validated inputs are checked before URL construction or signing side
effects. Preserve the InvalidHeaderValue behavior for all invalid inputs, and
add a regression test using SignQueryOptions with a NUL-containing value that
asserts InvalidHeaderValue.
In `@test/regression/issue/s3-header-injection.test.ts`:
- Around line 191-192: Update the raw TCP stub’s error handler near close() so
it records the socket error and causes the active test or request promise to
reject, rather than suppressing the failure. Wire every socket failure event to
the test’s existing rejection path while preserving the current
request-observation behavior.
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Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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📒 Files selected for processing (4)
src/runtime/webcore/s3/credentials_jsc.rssrc/s3_signing/credentials.rstest/js/bun/s3/s3-fd-validation.test.tstest/regression/issue/s3-header-injection.test.ts
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The check ran after the signature was computed and after the presign path had returned. A presigned URL therefore still embedded a NUL from accessKeyId or region in X-Amz-Credential. Run it before either path does any work, and include the presign response content type in it. The test stub now records socket errors, and presign has its own cases.
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I reviewed this PR and didn't find any bugs. The change is a small, well-tested tightening of existing validation, but since it touches the S3 signing / header-injection guard and changes presign() to throw on CR/LF credentials where it previously percent-encoded, a human look would still be worthwhile.
What was reviewed:
contains_invalid_header_value_byte—strings::contains_anywrapsindex_of_any, so this is the old check plus NUL; the local duplicate incredentials_jsc.rsis deleted and the crate re-export viapub use credentials::*resolves.- The moved sign-time check runs after
region,host,session_token, andcontent_md5are all derived, and before both the presign and header paths;content_typewas added to cover the presignresponse-content-typeparam. - Tests: fail-before shown on 1.4.0, positive control confirms valid credentials still sign; the raw-TCP stub and
{requests, errors}assertion pattern address the earlier CodeRabbit points.
Extended reasoning...
Overview
Two Rust source files and two test files. src/s3_signing/credentials.rs renames contains_newline_or_cr → contains_invalid_header_value_byte, makes it pub, adds NUL to the rejected byte set, and moves the sign-time validation block from after the presign early-return to before the authorization computation (adding content_type to the checked values). src/runtime/webcore/s3/credentials_jsc.rs drops its local duplicate, imports the shared helper, and updates three error messages. The two test files add proxy-env blanking and 10 new NUL/presign cases plus a positive control.
Security risks
This is a security hardening — it closes a gap where NUL bytes in S3 credentials/options reached raw picohttp headers, which fetch() would have rejected. The change strictly tightens validation: nothing previously rejected is now accepted, and the check now also covers the presign path. No security check is removed. The one nuance is that presign() with CR/LF in a credential now throws ERR_S3_INVALID_SIGNATURE instead of returning a percent-encoded (and useless) URL; this is called out in the PR description and is the correct behavior.
Level of scrutiny
Medium-high. The mechanical delta is trivial (one byte added to a byte-set scan, one block moved ~330 lines earlier, one duplicate deleted), but it lives in the S3 SigV4 signing path and header-injection guard. Per the approval guidelines, security-sensitive code paths warrant a human reviewer even when the automated pass finds nothing.
Other factors
The bug-hunting system found nothing. All three earlier bot review points (paragraph-long comment, presign path bypassed, empty socket error handler) were addressed in follow-up commits and CodeRabbit confirmed each. The tests follow repo conventions (raw Bun.listen stub with a comment explaining why Bun.serve can't observe the failure, test.each matrix, positive control, proxy-env isolation copied from proxy.test.ts). I verified strings::contains_any is index_of_any(...).is_some() so the helper is semantically the old check plus \0, and that pub use credentials::* in src/s3_signing/lib.rs makes the new import in credentials_jsc.rs resolve.
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Problem
sessionToken: "FAKE\0TOKEN"is sent asx-amz-security-token: FAKE\0TOKEN. Same foraccessKeyIdandregion(inAuthorization),contentDispositionandcontentEncoding.fetch()rejects these values.src/runtime/webcore/s3/credentials_jsc.rs:254(options) andsrc/s3_signing/credentials.rs:811(signing). The signing check also ran afterpresign()returned, so presigned URLs embedded the byte inX-Amz-Credential.Fix
contains_invalid_header_value_byteinbun_s3_signing, rejects NUL, CR and LF. Both checks use it. The option error now readsmust not contain CR/LF or NUL characters.presign(), env credentials ands3://URLs all get the same rule.ERR_S3_INVALID_SIGNATUREas for CR/LF today.presign()with CR/LF in a credential now throws instead of percent-encoding it.test/regression/issue/s3-header-injection.test.ts(10 new tests, all fail on 1.4.0),test/js/bun/s3/s3-fd-validation.test.ts, and the other local S3 suites.Background
S3Credentials::sign_request(src/s3_signing/credentials.rs) buildsAuthorizationand the other headers as raw picohttp headers. The HTTP client validates the URL, not the headers.get_credentials_with_options(credentials_jsc.rs) parses the JS options object. It is the only place that can name the bad option.Bun.listenstub.Bun.serveanswers 400 to a NUL header beforefetch()runs, so it cannot show whether the client sent anything.Notes
Found while going through a fuzz report on the S3 client. The rest of that report is already covered by open PRs: NO_PROXY and HTTPS_PROXY selection (#32046), 3xx handling (#35869), no content decoding on reads (#35871). Startup-only env credentials are documented behavior (
docs/runtime/s3.mdx) and #39210 reworks that area.Probe on bun 1.4.0 against a raw TCP stub.
fetch()with the same header value throwsTypeError: Header 'x-amz-security-token' has invalid value. The S3 client sent:typewith a NUL was already replaced byapplication/octet-streamthrough Blob type normalization. It is included in the option check for consistency with CR/LF.Presign on 1.4.0 returned
...X-Amz-Credential=AKIA\^@FAKE%2F...for a NUL inaccessKeyIdand the same forregion. The token and the response overrides were percent-encoded. The check now runs before either path does any signing work, and it includes the presign response content type. The four presign tests fail on the first commit of this PR and pass on the current one.Keys, bucket names and list parameters are percent-encoded. Endpoints with a NUL, CR, LF or space are rejected by the HTTP client as
InvalidURL. The multipart upload id from the server is validated inmultipart.rs. None of those needed a change.Both test files now blank the proxy env vars for their duration, the same way
test/js/bun/http/proxy.test.tsdoes. The S3 client sends loopback requests through an ambientHTTP_PROXY(#32046 covers that), so without this the local servers in these files never see a request in an environment with a proxy configured.Other suites run with the debug build:
s3-list-objects,s3-argument-validation,s3-requester-pays,s3-storage-class,s3-insecure,s3-numeric-options-coerce,s3-queueSize-validation,s3-connection-close,s3-list-checksum-algorithm, and the local blocks ofs3.test.ts. Twos3-list-objectstests timed out once each on a loaded machine right after the 40k-entry "big responses" test and pass alone in well under 100 ms. They do not touch the changed code.Fail-before output on 1.4.0:
With the fix: 18 pass in that file, 2 pass in
s3-fd-validation.test.ts. The test stub records socket errors and each test asserts on requests and errors together.[review] gate passed · iteration 1 · 4 files touched
fails on main (without fix)
passes on PR (with fix)
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gate history · 1 passed · 1 rejected · iteration 1
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