fluent-plugin-s3: Denial of Service (DoS) via Decompression Bomb in `in_s3`

published 2026-06-26 4 mo ago modified 2026-09-30 39 d ago also GHSA-xv9w-7v6q-hpjh , EUVD-2026-77705

cvss: 2.7; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits: 0; none known

fluent-plugin-s3 is an Amazon S3 input and output plugin for Fluentd. From 0.7.0 to 1.8.4, the in_s3 input plugin reads the entire decompressed payload of gzip, lzma2, and lzop objects into memory without enforcing a decompression_size_limit. An attacker with permission to upload objects to the monitored S3 bucket can provide a highly compressed object that expands excessively when Fluentd processes it. The resulting memory exhaustion can cause the operating system to terminate the Fluentd process and disrupt all log collection on the affected node. This issue is fixed in version 1.8.5.

Patch / fix

fixed in 1 links 2

rubygems fluent-plugin-s3 1.8.5

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 55 d ago (2026-09-14)

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	2.7	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L
GitHub	3.1	2.7	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem	package	affected	fixed in
rubygems	fluent-plugin-s3	>=0.7.0, <1.8.5	1.8.5

Affected products

fluent fluent-plugin-s3

Classification

Weakness

CWE-409 Improper Handling of Highly Compressed Data (Data Amplification)
CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary