# CVE-2026-16434: Adminer before 5.5.1 X-Forwarded-Prefix Backslash Bypass

> Attackers can bypass X-Forwarded-Prefix validation to manipulate cookie paths, requiring a misconfigured reverse proxy.

- **Severity:** Low 2.3 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 25 Aug 2026
- **Updated:** 27 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-16434, GHSA-fr74-9mf9-gf44, GHSA-jh7j-hfxx-jv6m, UBUNTU-CVE-2026-16434

## What is CVE-2026-16434?

CVE-2026-16434 is a low-severity vulnerability in vrana adminer, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-16434?


## How do I fix CVE-2026-16434?

Upgrade to a fixed version.

## Is CVE-2026-16434 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-16434 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-16434 and fix it if it is affected.

What it is: CVE-2026-16434 is a low-severity vulnerability in vrana adminer, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-16434 exists.

Affected product: vrana adminer. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-16434/ (Markdown: https://insights.sbomify.com/CVE-2026-16434/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-16434
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-16434
- OSV: https://osv.dev/vulnerability/CVE-2026-16434

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-16434/
Summaries are generated and may contain mistakes; the official description above is the record.