---
id: CVE-2026-16434
title: >-
  Adminer 4.6.0 through 5.5.0 (fixed in 5.5.1) contains an incomplete fix for a
  prior X-Forwarded-Prefix vulnerability (GHSA-8478-xrj3-h9c2)
summary: >-
  Adminer 4.6.0 through 5.5.0 (fixed in 5.5.1) contains an incomplete fix for a
  prior X-Forwarded-Prefix vulnerability (GHSA-8478-xrj3-h9c2). The validation
  guard (bootstrap.inc.php) only rejects prefixes matching ^/[^/], blocking
  //evil.c…
severity: none
cwe:
  - CWE-20
published: '2026-08-25'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:23:49.880'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-16434'
references:
  - url: 'https://github.com/vrana/adminer/security/advisories/GHSA-fr74-9mf9-gf44'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/adminer-before-x-forwarded-prefix-backslash-bypass
    label: disclosure@vulncheck.com
  - url: 'https://github.com/vrana/adminer/security/advisories/GHSA-fr74-9mf9-gf44'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00385
epssPercentile: 0.29696
ingestedAt: '2026-09-08T21:11:12.285Z'
---

## Overview

Adminer 4.6.0 through 5.5.0 (fixed in 5.5.1) contains an incomplete fix for a prior X-Forwarded-Prefix vulnerability (GHSA-8478-xrj3-h9c2). The validation guard (bootstrap.inc.php) only rejects prefixes matching ^/[^/], blocking //evil.com but allowing values such as /\evil.com whose second character is a backslash. Because browsers normalize backslash to forward slash, a network-path reference survives into REQUEST_URI and reaches cookie_path(), affecting the Set-Cookie Path attribute. Exploitation requires that clients can set the X-Forwarded-Prefix header (a misconfigured or absent reverse proxy). Impact is limited to anomalous cookie-path scoping.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.