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

What is CVE-2026-47321?

CVE-2026-47321 is a high-severity denial of service vulnerability in Apache MINA, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-789, CWE-409

Which versions are affected by CVE-2026-47321?

How do I fix CVE-2026-47321?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-47321 being exploited?

There is no known exploitation of CVE-2026-47321 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-47321, GHSA-3c8x-fp36-75xv, RHLW-2026-2cb9a31c02a7f38b, UBUNTU-CVE-2026-47321.