CVE-2026-47321

The CompressionFilter class uses ZLib to deflate and inflate data sent and received. When we inflate incoming data, the filter does not control the resulting size, and create a buffer no matter what.

Some compressed data may have a compression ration greater than 1 thousand, leading to an exhaustion of the application memory, as we don't control the deflated size.

The fix adds such a control by allowing the application developer to provide a fixed size limit, which when reached throws an exception. It also allows the user to provide a compression ratio that should not be exceeded, protected the application from small inflated files that inflate in gigantic files, but with a grace limit for the resulting size (1Mb) to avoid false positive (like a very small file inflating with a high ratio, but resulting with a acceptable size, like a few thousands bytes)

For application using this feature, it is highly recommended to create the CompressionFilter and to pass the maximum limit as a forth constructor parameter, maxDecompressedSize:

public CompressionFilter(final boolean compressInbound, final boolean compressOutbound, final int compressionLevel, final int maxDecompressedSize)Optionally one can also provide a maxDecompressRatio fifth parameter, and a decompressRatioMinSize sixth parameter to allow small inflated files with a high compression ratio to still be accepted.

Here are the additional constructor:

public CompressionFilter(final boolean compressInbound, final boolean compressOutbound,

final int compressionLevel, final int maxDecompressedSize,

final long maxDecompressRatio, final long decompressRatioMinSize)

Also note that a fluent API has been added to spare the users the pain to call a constructor with that many parameters:

 CompressionFilter compressionFilter = new CompressionFilter()

    .setCompressionLevel(Zlib.COMPRESSION_MAX)

  .setMaxDecompressedSize(1_000_000)

  .setMaxDecompressRatio(100).

  .setDecompressRatioMinSize(100_000); 

Applications using Apache MINA are advised to upgrade and configure their CompressionFilter instance.