What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-14 · updated 2026-09-30
• Weakness: CWE-409

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 products

• http4k: before 4.51.0.0; from 5.0.0.0, < 5.42.0.0; from 6.0.0.0, < 6.49.0.0

References

• https://github.com/http4k/http4k/commit/2618fe08f9801353012561ae1f1382fa2d37bac9
• https://github.com/http4k/http4k/commit/9f9e02f8efbbe04e0c70f1c46eef5d9d9067ea5b
• https://github.com/http4k/http4k/releases/tag/6.49.0.0
• https://github.com/http4k/http4k/security/advisories/GHSA-g4w2-6h2r-3m3w

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