CVE-2020-14403

Vulnerability

An out-of-bounds access vulnerability exists in libvncserver/hextile.c in LibVNCServer versions before 0.9.13. The issue occurs when processing Hextile-encoded framebuffer updates; insufficient bounds checking allows reading or writing beyond allocated memory. [2]

Exploitation

An attacker with network access to a VNC server using LibVNCServer can send a specially crafted Hextile encoding message. No authentication is required if the server is configured to allow unauthenticated connections. The attacker must be able to send RFB protocol messages to the server.

Impact

Successful exploitation could lead to a denial of service (crash) or potentially arbitrary code execution, depending on the memory layout. The out-of-bounds access may also disclose sensitive information from server memory. [2]

Mitigation

The vulnerability is fixed in LibVNCServer version 0.9.13, released on 2020-06-17. Users should upgrade to this version or later. Distributions such as Ubuntu have released updated packages (e.g., USN-4434-1 for LibVNCServer and USN-4573-1 for Vino) that include the fix. [1][2]