Fluentd is Vulnerable to Server-Side Request Forgery (SSRF) via Placeholder Expansion in out_http

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.2 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:L

EPSS

• CVE-2026-44161: 0.44% estimated exploitation activity in the next 30 days; percentile 38.44 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

The outhttp output plugin allows the use of placeholders (such as ${tag}) in the endpoint configuration parameter. It was discovered that if the placeholder value is derived from untrusted user input, an attacker can maliciously control the destination hostname of the outbound HTTP requests made by Fluentd. Impact This vulnerability allows for a Server-Side Request Forgery (SSRF) attack. An unauthenticated attacker can force the Fluentd node to send HTTP requests to arbitrary internal services. This can lead to unauthorized access to internal APIs, data exfiltration, or the compromise of cloud metadata endpoints (e.g., AWS IMDS 169.254.169.254). Patches v1.19.3 Workarounds If an immediate upgrade is not possible, users are strongly advised to apply the following mitigations: 1. Avoid Dynamic Hostnames Do not use the placeholder in the endpoint parameter as hostname. 2. Restrict Network Access Use firewall rules (e.g., iptables, AWS Security Groups) to block the Fluentd node from…

Published by the source

26 Jun 2026, 16:36 UTC

Last modified by the source

26 Jun 2026, 16:36 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-72f5-rr8c-r6gr

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# Patch Next advisory brief: CVE-2026-44161

Advisory: Fluentd is Vulnerable to Server-Side Request Forgery (SSRF) via Placeholder Expansion in `out_http`
IDs: CVE-2026-44161, GHSA-72f5-rr8c-r6gr
Record: https://patchnext.com/advisories/cve-2026-44161 (revision 1, source checked 26 Oct 2026, 15:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fluentd 1.19.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems fluentd: affected <= 1.19.2; fixed in 1.19.3

## Suggested inspection (read-only)
- RubyGems fluentd: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fluentd.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-72f5-rr8c-r6gr (GitHub-reviewed advisory GHSA-72f5-rr8c-r6gr lists affected ranges: RubyGems fluentd >=0 <=1.19.2)

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