Vulnerability-Lookup

CVE-2026-53659 (GCVE-0-2026-53659)

Vulnerability from cvelistv5 – Published: 2026-09-14 17:29 – Updated: 2026-09-14 19:03

Title

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

Summary

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.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-14 19:03 UTC

CWE

CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/http4k/http4k/security/advisor…	x_refsource_CONFIRM
https://github.com/http4k/http4k/commit/2618fe08f…	x_refsource_MISC
https://github.com/http4k/http4k/commit/9f9e02f8e…	x_refsource_MISC
https://github.com/http4k/http4k/releases/tag/6.49.0.0	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
http4k	http4k	Affected: < 4.51.0.0 Affected: >= 5.0.0.0, < 5.42.0.0 Affected: >= 6.0.0.0, < 6.49.0.0	guessed

Show details on NVD website

JSON

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FKIE_CVE-2026-53659

Vulnerability from fkie_nvd - Published: 2026-09-14 18:17 - Updated: 2026-09-14 19:17

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

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

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "vendor": "http4k",
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GHSA-G4W2-6H2R-3M3W

Vulnerability from github – Published: 2026-08-17 21:52 – Updated: 2026-08-17 21:58

Summary

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

Details

Impact

ServerFilters.GZip and RequestFilters.GunZip (and the underlying Gzip functions used to decompress request bodies) did not impose any cap on the decompressed size. A small malicious gzip-encoded request body (on the order of kilobytes) could decompress to gigabytes, exhausting the JVM heap and denying service to other clients.

Who is affected: any http4k server that accepts gzip-encoded requests via ServerFilters.GZip or RequestFilters.GunZip. Exploitable by any unauthenticated client. The vulnerability was introduced on 2017-08-01 (commit 2618fe08f9) and was present for ~9 years.

Patches

Line	Fixed in	Edition
v6.x (Community)	6.49.0.0	Community
v5.x (LTS)	5.42.0.0	Enterprise — contact enterprise@http4k.org
v4.x (LTS)	4.51.0.0	Enterprise — contact enterprise@http4k.org

The fix caps decompression at 10MB by default; oversized requests through ServerFilters.GZip / RequestFilters.GunZip now return 413 Request Entity Too Large, and decompressing elsewhere throws SizeLimitExceededException. The keyed hmacSHA256 helper and other safe paths are unaffected.

Workarounds

For deployments that cannot upgrade immediately: - Replace the GZip / GunZip filters with custom versions that wrap the decompressed InputStream in a size-limited reader, or - Strip gzip-encoded request support at the edge (CDN, reverse proxy, or load balancer).

References

Vulnerability introduced: 2618fe08f9
Fix release: v6.49.0.0
Background: CWE-409 — Improper Handling of Highly Compressed Data

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

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        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "4.48.2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53659"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-409"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-17T21:52:27Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Impact\n\n`ServerFilters.GZip` and `RequestFilters.GunZip` (and the underlying `Gzip` functions used to decompress request bodies) did not impose any cap on the decompressed size. A small malicious gzip-encoded request body (on the order of kilobytes) could decompress to gigabytes, exhausting the JVM heap and denying service to other clients.\n\n**Who is affected:** any http4k server that accepts gzip-encoded requests via `ServerFilters.GZip` or `RequestFilters.GunZip`. Exploitable by any unauthenticated client. The vulnerability was introduced on 2017-08-01 (commit `2618fe08f9`) and was present for ~9 years.\n\n### Patches\n\n| Line | Fixed in | Edition |\n|------|----------|---------|\n| v6.x (Community) | **6.49.0.0** | Community |\n| v5.x (LTS) | **5.42.0.0** | Enterprise \u2014 contact [enterprise@http4k.org](mailto:enterprise@http4k.org) |\n| v4.x (LTS) | **4.51.0.0** | Enterprise \u2014 contact [enterprise@http4k.org](mailto:enterprise@http4k.org) |\n\nThe fix caps decompression at 10MB by default; oversized requests through `ServerFilters.GZip` / `RequestFilters.GunZip` now return `413 Request Entity Too Large`, and decompressing elsewhere throws `SizeLimitExceededException`. The keyed `hmacSHA256` helper and other safe paths are unaffected.\n\n### Workarounds\n\nFor deployments that cannot upgrade immediately:\n- Replace the `GZip` / `GunZip` filters with custom versions that wrap the decompressed `InputStream` in a size-limited reader, or\n- Strip gzip-encoded request support at the edge (CDN, reverse proxy, or load balancer).\n\n### References\n\n- Vulnerability introduced: [`2618fe08f9`](https://github.com/http4k/http4k/commit/2618fe08f9)\n- Fix release: [v6.49.0.0](https://github.com/http4k/http4k/releases/tag/6.49.0.0)\n- Background: [CWE-409 \u2014 Improper Handling of Highly Compressed Data](https://cwe.mitre.org/data/definitions/409.html)",
  "id": "GHSA-g4w2-6h2r-3m3w",
  "modified": "2026-08-17T21:58:23Z",
  "published": "2026-08-17T21:52:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/http4k/http4k/security/advisories/GHSA-g4w2-6h2r-3m3w"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/http4k/http4k"
    },
    {
      "type": "WEB",
      "url": "https://github.com/http4k/http4k/releases/tag/6.49.0.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoS"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-53659 (GCVE-0-2026-53659)

FKIE_CVE-2026-53659

GHSA-G4W2-6H2R-3M3W

Impact

Patches

Workarounds

References

Tags

Sightings

Nomenclature