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Vulnerability · Published Sep 14, 2026 · Assigned by GitHub_M

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

High 7.5

In plain English

A high-severity security flaw in http4k from http4k. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.6%top 49.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Mavenorg.http4k:http4k-core6.49.0.0GHSA-g4w2-6h2r-3m3w
Mavenorg.http4k:http4k-core5.42.0.0GHSA-g4w2-6h2r-3m3w
Mavenorg.http4k:http4k-coreno fix listedGHSA-g4w2-6h2r-3m3w

Affected products (as reported)

VendorProductVersions
http4k http4k < 4.51.0.0>= 5.0.0.0, < 5.42.0.0>= 6.0.0.0, < 6.49.0.0

Weakness: CWE-409 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References