Bas Levering

Security researcher & sysadmin · Netherlands · healthcare IT. Disclosed CVEs in identity / auth stacks. Building public research notes here.

A substring match that turns Keycloak's policy enforcer off

CVE-2026-9800 — Keycloak’s policy enforcer used a substring match to detect its own access-denied page, so any authenticated user could append that path and skip every authorization check. The first package I ever audited, and a .contains() that lets everyone in.

June 29, 2026 · 6 min · 1171 words · Bas Levering

A pre-auth heap overflow in libvncclient's Tight decoder

GHSA-v9pm-47h4-jcq8 — a malicious VNC server can crash or take over any client built on libvncclient, default build, no auth. My first CVE, and why the client trusting the server is the whole problem.

May 29, 2026 · 6 min · 1263 words · Bas Levering

hello

First post. What this site is.

May 28, 2026 · 1 min · 56 words · Bas Levering