In Shadow 4.13 it is possible to inject control characters into fields provided to the SUID program chfn (change finger). Although it is not possible to exploit this directly (e.g. adding a new user fails because \n is in the block list) it is possible to misrepresent the /etc/passwd file when viewed. Use of \r manipulations and Unicode characters to work around blocking of the : character make it possible to give the impression that a new user has been added. In other words an adversary may be able to convince a system administrator to take the system offline (an indirect social-engineered denial of service) by demonstrating that "cat /etc/passwd" shows a rogue user account.

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