# Fabio allows HTTP clients to manipulate custom headers it adds

Advisory record · `GHSA-q7p4-7xjv-j3wf`

- **Identifiers:** `GHSA-q7p4-7xjv-j3wf` · `CVE-2025-48865` · `GO-2025-3722`
- **State:** Confirmed
- **Severity:** CVSS 9.1 Critical
- **Critical:** Yes: CVSS 9+
- **Weakness (CWE):** [CWE-345](https://cwe.mitre.org/data/definitions/345.html) · [CWE-348](https://cwe.mitre.org/data/definitions/348.html)
- **Tags:** [CWE-345](https://agentprime.io/advisories/tag/cwe-345.md) · [CWE-348](https://agentprime.io/advisories/tag/cwe-348.md)
- **Published:** 29 May 2025
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 29 May 2025, 16:50 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Critical

Critical, because:

- CVSS score 9.1: 9.0 or more.

How we decide what’s critical: <https://agentprime.io/advisories/critical.md>

## Affected packages

- `github.com/fabiolb/fabio` (Go): affected `<1.6.6`; fixed in `1.6.6`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Fabio versions before 1.6.6 are vulnerable. A client can list headers such as X-Forwarded-Host, X-Forwarded-Port, X-Forwarded-Proto, X-Real-Ip and Forwarded in the Connection header, which causes Fabio to strip them before the request reaches the backend. A backend that trusts these headers for access control could then be bypassed. Upgrade to Fabio 1.6.6 or later.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 9.1 Critical, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0047, the 40th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:14 UTC: First seen by agentprime
- 31 Oct 2026, 14:14 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-q7p4-7xjv-j3wf)

## Sources

- [GitHub Advisory Database: GHSA-q7p4-7xjv-j3wf](https://github.com/advisories/GHSA-q7p4-7xjv-j3wf)
- [OSV: GHSA-q7p4-7xjv-j3wf](https://osv.dev/vulnerability/GHSA-q7p4-7xjv-j3wf)
- <https://github.com/fabiolb/fabio/security/advisories/GHSA-q7p4-7xjv-j3wf>
- <https://nvd.nist.gov/vuln/detail/CVE-2025-48865>
- <https://github.com/fabiolb/fabio/commit/fdaf1e966162e9dd3b347ffdd0647b39dc71a1a3>
- <https://github.com/fabiolb/fabio>
- <https://github.com/fabiolb/fabio/releases/tag/v1.6.6>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-q7p4-7xjv-j3wf>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-q7p4-7xjv-j3wf/>. Everything for agents: <https://agentprime.io/llms.txt>.