# CVE-2026-47321: Apache MINA CompressionFilter decompression bomb DoS

Source: https://junglewise.ai/threats/cve-2026-47321-the-compressionfilter-class-uses-zlib-to-deflate-and-inflate-data  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-21. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-47321 · Severity: high · CVSS 7.5 · Published 2026-09-21

Apache MINA's CompressionFilter class does not limit the size of data after decompression, allowing an attacker to send highly compressed payloads that expand to enormous sizes and exhaust application memory. This causes denial of service by crashing applications that process untrusted compressed data without proper safeguards.

Technologies: [Apache Mina](https://junglewise.ai/threats/technologies/mina). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-47321 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-47321 being exploited in the wild.

**How severe is CVE-2026-47321?** High severity, with a CVSS score of 7.5, published 21 September 2026.

**Which products and versions are affected?** Apache Mina versions prior to fix.

**Is there a fix for CVE-2026-47321?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-47321 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-47321?** Check whether you run Apache Mina at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The CompressionFilter uses ZLib to decompress incoming data but fails to enforce limits on the decompressed output size or compression ratio, enabling decompression bomb attacks where small compressed inputs expand to gigabytes of data. An attacker can send a crafted compressed payload over the network to trigger uncontrolled memory allocation. The vulnerability is fixed by adding optional size and ratio limits via constructor parameters or a fluent API, with a 1MB grace threshold for small files.

## Affected products

- Apache MINA versions prior to fix

## Timeline

- 2026-09-21: disclosed

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