http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoS
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/GunZipfilters with custom versions that wrap the decompressedInputStreamin 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
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | org.http4k:http4k-core | >= 6.0.0.0, < 6.49.0.0, >= 5.0.0.0, < 5.42.0.0, <= 4.48.2.0 | 6.49.0.0, 5.42.0.0 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-409- Platform
- Java / Kotlin (Maven)
- Package
org.http4k:http4k-core- Disclosed
- 17.08.2026
- Updated
- 11.10.2026 12:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-g4w2-6h2r-3m3w - CC BY 4.0
Vulnerability history: org.http4k:http4k-core
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 4
- First → latest
- 06.2026 08.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 2
Disclosures per year
- 2026: 4
-
http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoS this entry
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