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High, CVSS 7.5

http4k: Unbounded gzip decompression in ServerFilters.GZip / RequestFilters.GunZip allowed memory-exhaustion DoS

CVE-2026-53659GHSA-g4w2-6h2r-3m3w

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Maven org.http4k:http4k-core

    Affected
    >= 5.0.0.0, < 5.42.0.0<= 4.48.2.0>= 6.0.0.0, < 6.49.0.0
    Fixed in
    5.42.0.0, 6.49.0.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-53659: 0.63% estimated exploitation activity in the next 30 days; percentile 50.23 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact ServerFilters.GZip and RequestFilters.GunZip (and the underlying Gzip functions used to decompress request bodies) did not impose any cap on the decompressed size. A small malicious gzip-encoded request body (on the order of kilobytes) could decompress to gigabytes, exhausting the JVM heap and denying service to other clients. Who is affected: any http4k server that accepts gzip-encoded requests via ServerFilters.GZip or RequestFilters.GunZip. Exploitable by any unauthenticated client. The vulnerability was introduced on 2017-08-01 (commit 2618fe08f9) and was present for ~9 years. Patches | Line | Fixed in | Edition | |------|----------|---------| | v6.x (Community) | 6.49.0.0 | Community | | v5.x (LTS) | 5.42.0.0 | Enterprise — contact enterprise@http4k.org | | v4.x (LTS) | 4.51.0.0 | Enterprise — contact enterprise@http4k.org | The fix caps decompression at 10MB by default; oversized requests through ServerFilters.GZip / RequestFilters.GunZip now return 413 Request Entity…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-g4w2-6h2r-3m3w

Agent brief

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# Patch Next advisory brief: CVE-2026-53659

Advisory: http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoS
IDs: CVE-2026-53659, GHSA-g4w2-6h2r-3m3w
Record: https://patchnext.com/advisories/cve-2026-53659 (revision 1, source checked 26 Oct 2026, 16:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: org.http4k:http4k-core 6.49.0.0, 5.42.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.http4k:http4k-core: affected >= 5.0.0.0, < 5.42.0.0; <= 4.48.2.0; >= 6.0.0.0, < 6.49.0.0; fixed in 5.42.0.0, 6.49.0.0

## Suggested inspection (read-only)
- Maven org.http4k:http4k-core: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.http4k:http4k-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-g4w2-6h2r-3m3w (GitHub-reviewed advisory GHSA-g4w2-6h2r-3m3w lists affected ranges: Maven org.http4k:http4k-core >=5.0.0.0 =0 =6.0.0.0 <6.49.0.0)

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