Date: Fri, 3 Nov 2017 12:25:12 +0000 From: Fiedler Roman <Roman.Fiedler@....ac.at> To: "'oss-security@...ts.openwall.com'" <oss-security@...ts.openwall.com> Subject: Re: Security risk of server side text editing in general and vim.tiny specifically > From: Jakub Wilk [mailto:jwilk@...lk.net] > > * Fiedler Roman <Roman.Fiedler@....ac.at>, 2017-11-03, 11:07: > >POC for vim.tiny on Ubuntu Xenial to overwrite arbitrary files as user > >root when editing file in directory owned by other user is available on > >request, disclosure after one week or if list discussion indicates > >other timing. > > By default, when vim wants to overwrite the file "foo", it does: > > rename("foo", "foo~") = 0 > open("foo", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0600) = 3 > > There's a race window between the two syscalls when the attacker could > re-create "foo", and then vim would happily write to it. > > Is this the attack you meant? This is one of the attack points, but there are multiple sequences of problematic syscalls, especially when running vim.tiny as root, also getxattr("x.txt", "system.posix_acl_access", ... -> get attrs of arbitrary file via symlink setxattr("x.txt", "system.posix_acl_access", ... -> set those attrs on arbitrary file chmod("x.txt", 0100644) = 0 -> set mode of previous x.txt on arbitrary file ... As previously stated, this indicates, that the "root-edits-file-of-non-root-user" use case was not considered. But is that a problem? Put it another way: when a doctor cuts himself with his scalpel, is it the doctor's or the scalpel's fault? LG Roman Download attachment "smime.p7s" of type "application/pkcs7-signature" (4814 bytes)
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