# CVE-2026-109584: Bandit HTTP/2 data amplification in HPACK decompression

Source: https://junglewise.ai/threats/cve-2026-109584-improper-handling-of-highly-compressed-data-data-amplification  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-26. Updated: 2026-10-26  
License: CC BY 4.0 with a link back

CVE-2026-109584 · Severity: info · Published 2026-10-26

Bandit is an HTTP/2 web server library for Elixir. An unauthenticated attacker can send a specially crafted HTTP/2 request with highly compressed headers that causes the server to allocate massive amounts of memory, exhausting available resources and causing a denial of service. A 49 KB malicious request can force servers to allocate 183 MB of memory before application code even runs.

Technologies: [Mtrudel Bandit](https://junglewise.ai/threats/technologies/mtrudel-bandit). Vendors: [Mtrudel](https://junglewise.ai/threats/vendors/mtrudel).

## Quick answers

**Is CVE-2026-109584 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109584 being exploited in the wild.

**How severe is CVE-2026-109584?** Informational severity, published 26 October 2026.

**Which products and versions are affected?** Mtrudel Bandit 0.3.3 to before 1.14.0.

**Is there a fix for CVE-2026-109584?** Yes: fixed in Bandit 1.14.0. Until then: Configure a finite max_header_list_size value to reject oversized decompressed header lists before memory allocation. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-109584 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-109584?** Check whether you run Mtrudel Bandit 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.

## How to fix

- Fixed in Bandit 1.14.0

Configure a finite max_header_list_size value to reject oversized decompressed header lists before memory allocation.

## Technical details

The vulnerability is a data amplification attack in HTTP/2 header decompression (HPACK). An attacker crafts a compressed HEADERS frame that stores one large cookie in the HPACK dynamic table, then references it thousands of times using 1-byte indexed fields. Bandit only validates the compressed block size (max_header_block_size) but never enforces the decompressed list limit (max_header_list_size, which defaults to infinity), and the combine_cookie_crumbs function concatenates all cookie fragments into a single binary, amplifying memory consumption. Each concurrent stream can repeat this attack independently.

## Affected products

- mtrudel Bandit 0.3.3 to before 1.14.0

## Timeline

- 2026-10-26: disclosed

## References

- [https://repo.hex.pm/](https://repo.hex.pm/)
- [https://github.com/](https://github.com/)

## Related threats

- [mtrudel bandit resource exhaustion in HTTP/2 request body reader](https://junglewise.ai/threats/cve-2026-116078-allocation-of-resources-without-limits-or-throttling)
- [mtrudel bandit HTTP/2 stream resource exhaustion](https://junglewise.ai/threats/cve-2026-115269-allocation-of-resources-without-limits-or-throttling)
- [mtrudel bandit WebSocket denial of service via fragmented messages](https://junglewise.ai/threats/cve-2026-114213-allocation-of-resources-without-limits-or-throttling)
- [mtrudel bandit inefficient algorithmic complexity in header parser](https://junglewise.ai/threats/cve-2026-113436-inefficient-algorithmic-complexity-vulnerability-in-the-header)
- [mtrudel bandit HTTP/2 handler resource limit bypass](https://junglewise.ai/threats/cve-2026-111103-improper-cleanup-on-thrown-exception-vulnerability-in-the-http-2)