[Bug] Potential DoS via Unbounded zlib.decompress (Zip Bomb Vulnerability) in Document Parser

[QiuYucheng2003]

Bug Description

A security vulnerability exists in the document parsing logic (specifically within the get_text_from_section method). Compressed data streams are being decompressed using zlib.decompress(data, -15) without any size limitations or memory boundaries.

This exposes the application to Decompression Bomb (Zip Bomb) attacks. An attacker can provide a maliciously crafted document (e.g., a manipulated HWP file) with a tiny compressed payload that expands to several gigabytes. When the parser attempts to read this file, it will cause a massive, instantaneous memory allocation, leading to an Out of Memory (OOM) crash and Denial of Service (DoS) for the host system or agent workflow.

Code Location:
base.py -> get_text_from_section method:
unpacked_data = (
zlib.decompress(data, -15) if self.is_compressed(load_file) else data
)

Version

main branch

Steps to Reproduce

Steps to Reproduce:
(Identified via static code analysis, theoretical reproduction steps below)

1. Supply a malicious composite document containing a highly compressed, repetitive byte-stream section (Zip bomb payload).

2. Invoke the reader/parser to process the document.

3. Observe the zlib.decompress function attempting to load the entire uncompressed payload into memory at once, instantly exhausting available RAM and triggering the OS OOM killer.

Relevant Logs/Tracebacks

[dosubot]

I can confirm this vulnerability exists in the HWP reader at llama-index-integrations/readers/llama-index-readers-hwp/llama_index/readers/hwp/base.py. The zlib.decompress(data, -15) call has no size limit, compression ratio check, or streaming safeguard.

A straightforward fix would be to use a zlib.decompobj with incremental decompression and enforce a maximum output size. For example:

MAX_DECOMPRESSED_SIZE = 100 * 1024 * 1024  # 100 MB limit (adjust as needed)

def _safe_decompress(self, data: bytes, max_size: int = MAX_DECOMPRESSED_SIZE) -> bytes:
    decompressor = zlib.decompressobj(-15)
    result = b""
    chunk = decompressor.decompress(data, max_size)
    result += chunk
    if decompressor.unconsumed_tail or not decompressor.eof:
        if len(result) >= max_size:
            raise ValueError(
                f"Decompressed data exceeds maximum allowed size ({max_size} bytes). "
                "Possible decompression bomb."
            )
    return result

Then replace the current line with:

unpacked_data = (
    self._safe_decompress(data) if self.is_compressed(load_file) else data
)

This limits memory allocation during decompression and raises a clear error for abnormally large payloads.

To reply, just mention @dosu.

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