shadow-utils (aka shadow) 4.4 through 4.17.0 establishes a default /etc/subuid behavior (e.g., uid 100000 through 165535 for the first user account) that can realistically conflict with the uids of users defined on locally administered networks, potentially leading to account takeover, e.g., by leveraging newuidmap for access to an NFS home directory (or same-host resources in the case of remote logins by these local network users). NOTE: it may also be argued that system administrators should not have assigned uids, within local networks, that are within the range that can occur in /etc/subuid.
Shadow-utils: possible password leak during passwd(1) change
A flaw was found in shadow-utils. When asking for a new password, shadow-utils asks the password twice. If the password fails on the second attempt, shadow-utils fails in cleaning the buffer used to store the first entry. This may allow an attacker with enough access to retrieve the password from the memory.
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 /
An issue was discovered in shadow 4.5. newgidmap (in shadow-utils) is setuid and allows an unprivileged user to be placed in a user namespace where setgroups(2) is permitted. This allows an attacker to remove themselves from a supplementary group, which may allow access to certain filesystem paths if the administrator has used "group blacklisting" (e.g., chmod g-rwx) to restrict access to paths. This flaw effectively reverts a security feature in the kernel (in particular, the /proc/self/setgroups knob) to prevent this sort of privilege escalation.
In shadow before 4.5, the newusers tool could be made to manipulate internal data structures in ways unintended by the authors. Malformed input may lead to crashes (with a buffer overflow or other memory corruption) or other unspecified behaviors. This crosses a privilege boundary in, for example, certain web-hosting environments in which a Control Panel allows an unprivileged user account to create subaccounts.