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CVE-2026-53659

high · CVSS 7.5Published 9/14/2026 at 06:17 PMCWE-409

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.G…

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.

Why it matters

Internet-facing
Not identified as a common internet-facing category
Exploitation likelihood
high
  • Remotely exploitable over the network — no physical or local access required
  • Low attack complexity — no special conditions needed to exploit
  • No authentication required
  • No user interaction needed — can be exploited automatically
Recommended mitigation

Apply the vendor patch as soon as it's available or already released.

This analysis is generated from structured CVSS vector data, CISA KEV cross-referencing, and vendor/product category rules — not a manual expert review. Treat it as a starting point, not a substitute for your own assessment.

CVSS Vector Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack Vector
Network
Complexity
Low
Privileges Req.
None
User Interaction
None

EU Vulnerability Database (ENISA)

EUVD ID
EUVD-2026-77694
View on EUVD

EUVD is ENISA's EU vulnerability database, still in beta. EPSS is a probabilistic exploitation-likelihood score, not a certainty.

View official CVE record

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