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  4. CVE 2026 53659 http4k unbounded gzip decompression in
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Back to active CVEs
High · CVSS 7.5CVE-2026-53659GHSA-G4W2-6H2R-3M3W

http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoSCVE-2026-53659

Answer in brief

CVE-2026-53659 records a High severity (CVSS 7.5) vulnerability in http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoS. The current sources do not mark it as known exploited. The current feed maps http4k/http4k (generic), org.http4k:http4k-core (maven), org.http4k:http4k-core (maven), org.http4k:http4k-core (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 14, 2026Updated Sep 30, 2026Source checked Oct 30, 2026First seen by HOL Aug 17, 2026Material review Sep 30, 2026
Upstream Advisory

Key facts

Risk
High · CVSS 7.5
Exploitation
Not marked as known exploited
Affected software
7 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps http4k/http4k (generic), org.http4k:http4k-core (maven), org.http4k:http4k-core (maven), org.http4k:http4k-core (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
http4k/http4kgeneric<4.51.0.0 || >=5.0.0.0 <5.42.0.0 || >=6.0.0.0 <6.49.0.04.51.0.0, 5.42.0.0, 6.49.0.0
org.http4k:http4k-coremaven>=5.0.0.0,<5.42.0.05.42.0.0
org.http4k:http4k-coremaven<=4.48.2.0Not reported
org.http4k:http4k-coremaven>=6.0.0.0,<6.49.0.06.49.0.0
org.http4k:http4k-coremaven>=6.0.0.0 <6.49.0.06.49.0.0
org.http4k:http4k-coremaven>=5.0.0.0 <5.42.0.05.42.0.0
org.http4k:http4k-coremaven>=0Not reported

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for http4k/http4k, org.http4k:http4k-core, org.http4k:http4k-core.
  2. 2Review the reported fix. Update http4k/http4k to 4.51.0.0; org.http4k:http4k-core to 5.42.0.0; org.http4k:http4k-core to 6.49.0.0; org.http4k:http4k-core to 6.49.0.0; org.http4k:http4k-core to 5.42.0.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Sep 14, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Sep 30, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Aug 17, 2026

Sources and claim methodology

  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
Upstream source description

http4k is a functional toolkit for Kotlin HTTP applications. Prior to 4.51.0.0, 5.42.0.0, and 6.49.0.0, ServerFilters.GZip, RequestFilters.GunZip, and the underlying Gzip request-body decompression functions impose no limit on decompressed size. An unauthenticated client can send a small gzip-encoded request body that expands to gigabytes, exhausting the JVM heap and denying service to other clients. The fix uses SizeLimitedInputStream to enforce a default 10 MiB limit, causes ServerFilters.GZip and RequestFilters.GunZip to return 413 Request Entity Too Large, and causes other decompression paths to throw SizeLimitExceededException. This issue is fixed in versions 4.51.0.0, 5.42.0.0, and 6.49.0.0.

Quoted source text, attributed separately from HOL analysis.

Record context

Vulnerability class
Missing Auth
EPSS
Not reported
CWE IDs
CWE-409
Source
CVE List V5
Source checked
Oct 30, 2026
References
6 linked sources
Open source record