---
title: "CVE-2025-48865: Fabio allows HTTP clients to manipulate custom headers it adds"
url: https://erroneo.us/security/cve/CVE-2025-48865/
description: "CVE-2025-48865 (github.com/fabiolb/fabio (Go)): Fabio is an HTTP(S) and TCP router for deploying applications managed by consul. Prior to version 1.6.6…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-05-30
date_modified: 2025-05-30
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-48865"
kev: false
cvss: 9.1
epss: 0.00451
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-48865: Fabio allows HTTP clients to manipulate custom headers it adds

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.5% , percentile 38: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 38% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/fabiolb/fabio (Go) <= 1.6.5, fixed in 1.6.6 . Check your lockfile, including transitive dependencies.

## What it is

Fabio is an HTTP(S) and TCP router for deploying applications managed by consul. Prior to version 1.6.6, 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. Some of these custom headers can 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. This issue has been patched in version 1.6.6.

## Affected packages

- Go `github.com/fabiolb/fabio` <= 1.6.5 → fixed: 1.6.6

## Affected products (CVE record)

- fabiolb fabio: < 1.6.6

## Severity

- GitHub_M CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.45% probability of exploitation activity in the next 30 days; percentile 38.

## Sources

- [GitHub Advisory GHSA-q7p4-7xjv-j3wf](https://github.com/advisories/GHSA-q7p4-7xjv-j3wf)
- [CVE.org record CVE-2025-48865](https://www.cve.org/CVERecord?id=CVE-2025-48865)
- [NVD entry CVE-2025-48865](https://nvd.nist.gov/vuln/detail/CVE-2025-48865)
- [github.com](https://github.com/fabiolb/fabio/security/advisories/GHSA-q7p4-7xjv-j3wf)
- [github.com](https://github.com/fabiolb/fabio/commit/fdaf1e966162e9dd3b347ffdd0647b39dc71a1a3)
- [github.com](https://github.com/fabiolb/fabio/releases/tag/v1.6.6)

---
Source page: https://erroneo.us/security/cve/CVE-2025-48865/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt