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.
| 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.
For deployments that cannot upgrade immediately:
GZip / GunZip filters with custom versions that wrap the decompressed InputStream in a size-limited reader, or2618fe08f9{
"cwe_ids": [
"CWE-409"
],
"github_reviewed": true,
"github_reviewed_at": "2026-08-17T21:52:27Z",
"nvd_published_at": null,
"severity": "HIGH"
}