Executive brief
Fluentd is a popular data collection tool used to gather and route logs from various sources to storage systems. A vulnerability in how it handles compressed data allows an attacker to send a specially crafted "zip bomb" that expands to an enormous size when processed. This can exhaust the server's memory, causing the Fluentd service to crash and disrupting all log collection and data forwarding operations.
Technical details
A denial-of-service vulnerability exists in Fluentd's in_http and in_forward plugins due to improper handling of highly compressed data (CWE-409). While the software enforces limits on the size of incoming compressed payloads (via body_size_limit and chunk_size_limit), it fails to validate the size of the data after decompression. An unauthenticated remote attacker can exploit this by sending a 'gzip bomb'—a small compressed file that expands significantly in memory—leading to memory exhaustion and an Out-of-Memory (OOM) kill of the process. The issue is addressed in version 1.19.3 by introducing a decompression_size_limit and processing data in 64KB chunks.
Affected products
- Fluent Fluentd < 1.19.3
Timeline
- 2026-06-25: patched: Fix merged and version 1.19.3 released.
- 2026-06-26: advisory: GitHub Security Advisory GHSA-j9cw-hwqf-85w7 published.
- 2026-07-08: disclosed: CVE-2026-44160 published to NVD.