CVE-2026-53659
HIGHDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Low risk: more likely to be exploited than 37% of all known CVEs.
References
Related Vulnerabilities
Other CWE-409 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2026-49975 | High | 7.5 | 34% | - | Fix |
| CVE-2026-21441 | High | 7.5 | 3.0% | - | Fix |
| CVE-2024-43499 | High | 7.5 | 2.6% | - | Fix |
| CVE-2024-28180 | Medium | 4.3 | 2.0% | - | Fix |
| CVE-2017-16129 | Medium | 5.9 | 1.8% | - | Fix |
| CVE-2022-29225 | High | 7.5 | 1.6% | - | Fix |
Common questions
How do I fix CVE-2026-53659?
No published fix for CVE-2026-53659 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-53659 being actively exploited?
Not that we know of. CVE-2026-53659 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.44% is the estimated probability that it will be exploited in the next 30 days. That is higher than 37% of all scored CVEs.
How severe is CVE-2026-53659?
CVE-2026-53659 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-14.