Mason Loring Bliss

**Name of the Vulnerable Software and Affected Versions** NLnet Labs Unbound versions up to and including 1.12.0 NLnet Labs NSD versions up to and including 4.3.3 **Description** The issue is related to a local vulnerability that allows for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. If the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. **Recommendations** For NLnet Labs Unbound versions up to and including 1.12.0, consider disabling the PID file writing functionality until a patch is available. For NLnet Labs NSD versions up to and including 4.3.3, restrict access to the PID file to minimize the risk of exploitation. As a temporary workaround, consider removing the symlink functionality for the PID file until a patch is available. At the moment, there is no information about a newer version that contains a fix for this vulnerability.