Fabio allows HTTP clients to manipulate custom headers it adds

Exploitation

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

CVSS

9.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2025-48865: 0.47% estimated exploitation activity in the next 30 days; percentile 40.41 (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.

Summary Fabio allows clients to remove X-Forwarded headers (except X-Forwarded-For) due to a vulnerability in how it processes hop-by-hop headers. Fabio adds HTTP headers like X-Forwarded-Host and X-Forwarded-Port when routing requests to backend applications. Since the receiving application should trust these headers, allowing HTTP clients to remove or modify them creates potential security vulnerabilities. However, it was found that some of these custom headers can indeed be removed and, in certain cases, manipulated. The attack relies on the behavior that headers can be defined as hop-by-hop via the HTTP Connection header. By setting the following connection header, the X-Forwarded-Host header can, for example, be removed: Similar critical vulnerabilities have been identified in other web servers and proxies, including CVE-2022-31813 in Apache HTTP Server and CVE-2024-45410 in Traefik. Details It was found that the following headers can be removed in this way (i.e. by specifying…

Published by the source

29 May 2025, 16:50 UTC

Last modified by the source

30 May 2025, 15:25 UTC

Source last checked

26 Oct 2026, 15:09 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-q7p4-7xjv-j3wf

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# Patch Next advisory brief: CVE-2025-48865

Advisory: Fabio allows HTTP clients to manipulate custom headers it adds
IDs: CVE-2025-48865, GHSA-q7p4-7xjv-j3wf
Record: https://patchnext.com/advisories/cve-2025-48865 (revision 1, source checked 26 Oct 2026, 15:09 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/fabiolb/fabio 1.6.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/fabiolb/fabio: affected <= 1.6.5; fixed in 1.6.6

## Suggested inspection (read-only)
- Go github.com/fabiolb/fabio: 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 github.com/fabiolb/fabio.
- 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-q7p4-7xjv-j3wf (GitHub-reviewed advisory GHSA-q7p4-7xjv-j3wf lists affected ranges: Go github.com/fabiolb/fabio >=0 <=1.6.5)

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