Bug 308712 – Binary key over-read in IndexedDB deserialization

• Component: DOM
• Status: RESOLVED FIXED

[Jarred Sumner]

I found this via Claude Code Security. Please don't credit me personally.

SUMMARY

In the binary key deserialization path of decodeKey() at Source/WebCore/Modules/indexeddb/server/IDBSerialization.cpp:354, Vector<uint8_t> dataVector(data) copies the entire remaining span into the vector, not just the declared size bytes. For compound array keys, the first binary sub-key's value includes the raw serialized bytes of all subsequent sub-keys.

DETAILS

At IDBSerialization.cpp:342-358:

  case SIDBKeyType::Binary: {
      uint64_t size64;
      if (!readLittleEndian(data, size64))
          return false;
      if (data.size() < size64)
          return false;
      if (size64 > std::numeric_limits<size_t>::max())
          return false;
      size_t size = static_cast<size_t>(size64);
      Vector<uint8_t> dataVector(data);       // BUG: copies ALL remaining bytes
      skip(data, size);                        // only advances by size bytes
      result.setBinaryValue(ThreadSafeDataBuffer::create(WTF::move(dataVector)));
      return true;
  }

The span cursor is correctly advanced by skip(data, size) for subsequent parsing, but dataVector already contains all trailing serialized data. For compound array keys [binaryKey1, binaryKey2], binaryKey1's value includes the raw serialized form of binaryKey2.

Introduced by: https://github.com/WebKit/WebKit/commit/2c844da0386ff67d69fe0982a84ef6df8533571b

SUGGESTED FIX

Change line 354 from Vector<uint8_t> dataVector(data) to Vector<uint8_t> dataVector(data.first(size)).

[Radar WebKit Bug Importer]

<rdar://problem/171246072>

[Anne van Kesteren]

Pull request: https://github.com/WebKit/WebKit/pull/59965

[EWS]

Committed 308694@main (a7aa0f525259): <https://commits.webkit.org/308694@main>

Reviewed commits have been landed. Closing PR #59965 and removing active labels.