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.
- 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
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
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.
Sources
Also known as DEBIAN-CVE-2026-16434, GHSA-fr74-9mf9-gf44, GHSA-jh7j-hfxx-jv6m, UBUNTU-CVE-2026-16434.