fix(serialization): bound msgpack decode nesting depth before allocation (LAB-2487) - #112
fix(serialization): bound msgpack decode nesting depth before allocation (LAB-2487)#11227Bslash6 wants to merge 3 commits into
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…ion (LAB-2487) @msgpack/msgpack 3.1.3 eagerly runs new Array(size) per collection header before children decode and has no depth limit, so nested headers stack preallocations disproportionate to input: a measured 15KB of forged array16 headers forced ~400MB of transient heap (~26,700x) before the end-of-input throw. boundedDecodeOptions caps each collection's declared size but cannot stop the depth-stacking, and the post-decode validateDepth runs after the allocations. Add assertDecodeDepth: a single-pass structural pre-scan (reads only headers, skips payloads, allocates nothing but a depth-bounded counter) that rejects input exceeding maxDepth or whose declared children exceed the bytes present (a global slot budget) before the decoder allocates. Wired at all three untrusted decode sites via the shared helper so the bound cannot drift: MessagePackSerializer.decode, decodeInteropValue, deserializeEvent. Also: give the fixed-schema invalidation-event path a least-privilege 4KB / depth-3 cap; add maxExtLength symmetry to boundedDecodeOptions. py (msgpack-python) and rs (rmp-serde) are already bounded by their libraries' depth limits (assessed, follow-up filed to make those bounds explicit). Regression tests pin the 5000-deep probe rejection, the spine/slot-budget reject, write/read symmetry to maxDepth, per-branch rejections, and a differential fuzz asserting the pre-scan is byte-faithful to the decoder across every msgpack type (no false-accept).
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WalkthroughThe PR adds a pre-decode MessagePack structural scan, applies depth and size limits to invalidation events and interop values, preserves fire-and-forget publish behaviour, and expands tests and documentation for malformed, nested, and untrusted payloads. ChangesSerialization bounds
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The change adds bounded validation before MessagePack decoding and tighter limits for invalidation events to prevent excessive nesting and allocation. No actionable merge-blocking risk remains, so the PR is merge-ready after normal checks and review. Sequence Diagram(s)sequenceDiagram
participant MessagePackSerializer
participant assertDecodeDepth
participant MessagePackDecoder
MessagePackSerializer->>assertDecodeDepth: scan payload structure and depth
assertDecodeDepth-->>MessagePackSerializer: return or raise SerializationError
MessagePackSerializer->>MessagePackDecoder: decode accepted payload
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In `@packages/cachekit/src/invalidation/event.ts`:
- Around line 62-66: Update serializeEvent to validate the encoded event size
against DEFAULT_MAX_INVALIDATION_EVENT_SIZE before returning the bytes, throwing
SerializationError with the encoded byte length and limit when exceeded. Keep
deserializeEvent’s existing validation unchanged.
In `@packages/cachekit/src/serialization/serializer.test.ts`:
- Around line 414-421: Update the random-garbage loop around assertDecodeDepth
to catch the thrown value and assert it is a SerializationError, rather than
recording a boolean and checking its type. Preserve the successful path and
ensure unexpected RangeError or TypeError failures are not accepted.
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packages/cachekit/README.mdpackages/cachekit/src/constants.tspackages/cachekit/src/invalidation/event.tspackages/cachekit/src/serialization/interop.tspackages/cachekit/src/serialization/serializer.test.tspackages/cachekit/src/serialization/serializer.ts
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…lker error type (LAB-2487) CodeRabbit remediation on #112: - serializeEvent now rejects events over DEFAULT_MAX_INVALIDATION_EVENT_SIZE. Without this, an oversized event passed the publisher and was rejected by every subscriber's deserializeEvent cap — invalidation silently lost, stale L1 served, no signal to the publisher. RedisInvalidationChannel.publish keeps its never-throw fire-and-forget contract by catching the rejection and logging it like transport failures (a best-effort invalidation must not fail the caller's write path; cache-core calls publish un-guarded). - The differential-fuzz random-garbage loop now asserts the walker rejects only via SerializationError, replacing a tautological typeof check — a RangeError/TypeError from a bad skip width or out-of-range DataView read (a walker fault) now fails the test instead of being swallowed.
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…487) The event timestamp is inert payload in these tests — nothing asserts on it — so a constant is the deterministic choice; matches the file's existing fixed-literal convention. Fixes all three occurrences, not just the one Kody flagged.
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What & why (LAB-2487)
Follow-on from #111 (LAB-281). That PR bounded each collection's declared size on decode, but a residual remained:
@msgpack/msgpack3.1.3 eagerly runsnew Array(size)for every array header before its children decode, and has no nesting-depth limit (the serializer'svalidateDepthruns post-decode, after the allocations). So nested headers stack preallocations disproportionate to input.Measured (real probe,
@msgpack/msgpack3.1.3, shipped bounds): 5000 nestedarray16(10000)headers = 15 KB input → ~400 MB transient heap (~26,700×) before the end-of-input throw. A backend-write attacker needs only a few KB of forged bytes to OOM the reader. Latest published version is 3.1.3 andmainstill has nomaxDepthoption, so this cannot be closed by decode options.The fix
assertDecodeDepth(data, maxDepth)— a single-pass structural pre-scan run beforedecode(). It reads only headers, skips payloads, materialises nothing, and allocates only a depth-bounded counter. It rejects input that:maxDepth(the stack-recursion vector), orIt fails closed: any unknown head byte, truncation, or trailing bytes →
SerializationError, so a pre-scan/decoder desync can only ever reject (availability), never admit bytes the decoder would amplify. Wired at all three untrusted decode sites through the shared helper so the bound cannot drift:MessagePackSerializer.decode,decodeInteropValue,deserializeEvent. After the fix the 15 KB probe is rejected in <1 MB.Also in this PR:
deserializeEventis now held to a 4 KB / depth-3 cap instead of the 10 MB value ceiling.maxExtLengthsymmetry added toboundedDecodeOptions.Cross-SDK assessment (AC-3)
@msgpack/msgpack3.1.3msgpack-python1.2.1StackErrorat ~1024 nesting → hard 82 MB ceiling regardless of input;StackErroris aValueErrorsubclass and is caught → cache-missrmp-serde1.xDepthLimitExceeded), no eager header preallocationpy/rs are bounded today, but by their libraries' defaults, not by an owned cachekit invariant — a follow-up makes those explicit and regression-tests them.
Known residual (separate concern)
Even with the depth bound, a legal payload still materialises ~40× its bytes into objects (measured 9 MB → 365 MB). That is bounded by the untrusted-decode input-size cap, not by any depth/element rule — it's a
maxDecodedSize-sizing decision (documented in the README security note, escalated separately with a concurrency-aware framing). This PR closes the unbounded amplifier; the 40× residual is a cap-sizing call, not a structural hole.Review
Passed an expert panel (bug-hunter, security, code-craftsman, catchphrase) + an adversarial design panel (security, red-team). Bug-hunter and craftsman hand-traced the walker byte-for-byte against
@msgpack/msgpack3.1.3's decoder source and found no false-accept; security confirmed complete entry-point coverage and fail-closed propagation. Their non-blocking findings (fuzz coverage across every type, event cap,maxExtLength, per-branch reject tests) are applied here.Tests
serializer.test.tsLAB-2487 block: the 5000-deep probe rejection, the spine/slot-budget reject, write/read symmetry tomaxDepth, per-branch rejections, and a differential fuzz (500 legal values across every msgpack head-byte family incl. bin/int64/float64/ext-timestamp/array16/map16 + 500 garbage buffers) asserting the pre-scan is byte-faithful to the decoder. Full suite: no new failures (the 16 reds are the pre-existing 0.1.2-prebuilt-vs-0.1.3-source core gap, unrelated).Docs
Serializer DoS-protection docstring updated (four → five layers); README value-size section gained a security note on
maxDecodedSizeas a decode-time memory bound. No executable-doc runner in cachekit-ts, so no doctest surface to update.Summary by CodeRabbit
Security
Bug Fixes
Documentation