CVE-2026-53659Network attack vector

Unauthenticated service interruption via unbounded gzip decompression

Published Sep 14, 2026 · Updated Sep 14, 2026

Denial of service in http4k 4.50.0.0 and earlier, 5.0.0.0 through 5.41.0.0, and 6.0.0.0 through 6.48.0.0 allows remote attackers to interrupt service. ServerFilters.GZip, RequestFilters.GunZip, and underlying gzip functions decompress request bodies without an output-size cap, allowing kilobytes of compressed input to consume gigabytes of JVM heap. Any unauthenticated client can reach the flaw when a server accepts gzip-encoded requests through these paths; exploitation exhausts memory and denies service to other clients.

CVSS severity7.5
High
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in http4k 4.50.0.0 and earlier, 5.0.0.0 through 5.41.0.0, and 6.0.0.0 through 6.48.0.0 allows remote attackers to interrupt service. ServerFilters.GZip, RequestFilters.GunZip, and underlying gzip functions decompress request bodies without an output-size cap, allowing kilobytes of compressed input to consume gigabytes of JVM heap. Any unauthenticated client can reach the flaw when a server accepts gzip-encoded requests through these paths; exploitation exhausts memory and denies service to other clients.

The record

CVE
CVE-2026-53659
Published
Sep 14, 2026
Updated
Sep 14, 2026
Vendor
http4k Ltd
Product
http4k
Classifications
CWE-409, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.51.0.0
  2. Affected versionversion=>= 5.0.0.0, < 5.42.0.0
  3. Affected versionversion=>= 6.0.0.0, < 6.49.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

http4k Ltd · http4kversion=< 4.51.0.0; version=>= 5.0.0.0, < 5.42.0.0; version=>= 6.0.0.0, < 6.49.0.0

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-409Improper Handling of Highly Compressed Data (Data Amplification)
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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