CVE-2026-33999 Details

An integer underflow vulnerability has been identified in the X.Org X server, specifically within the XKB compatibility map handling. This flaw allows an attacker with local or remote access to the X11 server to exploit a buffer read overrun, leading to memory-safety violations. The vulnerability can cause a denial-of-service (DoS) condition or other severe impacts, depending on the context in which X.Org or Xwayland is deployed.

To mitigate this vulnerability, restrict access to the X11 server. For remote access, disable X11 forwarding in SSH configurations if not needed. After updating the SSH configuration, restart the sshd service. Note that disabling X11 forwarding may affect remote graphical applications.