The account management of the CVS pserver (which is used to give remote access to CVS repositories) uses a CVSROOT/passwd file in each repository which contains the accounts and their authentication information as well as the name of the local unix account to use when a pserver account is used. Since CVS performed no checking on what unix account was specified anyone who could modify the CVSROOT/passwd could gain access to all local users on the CVS server, including root.
This has been fixed in upstream version 1.11.11 by preventing pserver from running as root. For Debian this problem is solved in version 1.11.1p1debian-9 in two different ways:
Additionally, CVS pserver had a bug in parsing module requests which could be used to create files and directories outside a repository. This has been fixed upstream in version 1.11.11 and Debian version 1.11.1p1debian-9.
Finally, the umask used for “cvs init” and “cvs-makerepos” has been changed to prevent repositories from being created with group write permissions.
MD5 checksums of the listed files are available in the original advisory.