Muhammara has a NULL pointer dereference in LZWDecode filter when DecodeParms omits EarlyChange key

Summary

## Summary A NULL pointer dereference vulnerability exists in `PDFParser::CreateFilterForStream()` when processing a PDF stream with `/Filter /LZWDecode` and a `/DecodeParms` dictionary that does not contain the `EarlyChange` key. This causes an access violation (0xC0000005) and crashes the process. ## Affected Version muhammara <= 6.0.4 (latest) ## Vulnerability Details **File:** `src/deps/PDFWriter/PDFParser.cpp` line 2107 ```cpp if (inDecodeParams) { PDFObjectCastPtr<PDFInteger> earlyObj( QueryDictionaryObject(inDecodeParams, "EarlyChange") ); early = earlyObj->GetValue(); // NULL dereference when EarlyChange key is absent } ``` When `inDecodeParams` is non-NULL but lacks the `EarlyChange` key: 1. `QueryDictionaryObject()` returns NULL 2. `PDFObjectCastPtr<PDFInteger>(NULL)` wraps NULL 3. `earlyObj->GetValue()` dereferences NULL → crash ## PoC 460-byte malicious PDF triggers crash via `startReadingFromStream()`: - PDF contains `/Filter /LZWDecode` with `/DecodeParms << >>` (empty, no EarlyChange) - Exit code: `0xC0000005` (Access Violation) ## Fix ```cpp if (earlyObj) early = earlyObj->GetValue(); ``` ## Impact Any application accepting untrusted PDFs and using muhammara to read stream contents is vulnerable to DoS. Similar to: CVE-2022-41957, CVE-2022-39381 ## PoC File [poc_muhammara_lzw_null.js](https://github.com/user-attachments/files/27186113/poc_muhammara_lzw_null.js)