CVE-2026-47321: Apache MINA: Unbounded Decompression Amplification DoS in Zlib.inflate

[Emmanuel Lécharny <elecharny () apache org>]

Severity: 

Affected versions:

- Apache MINA (org.apache.mina:mina-filter-compression) 2.2.0 before 2.2.8
- Apache MINA (org.apache.mina:mina-filter-compression) 2.1.0 before 2.1.13
- Apache MINA (org.apache.mina:mina-filter-compression) 2.0.0 before 2.0.29

Description:

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.

Credit:

Venkatraman Kumar, SecurIn (finder)

References:

https://lists.apache.org/thread/y7xj1bl8qo47p9bktb11hg5v6k1d4dyj
https://mina.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-47321