Date: Tue, 31 Oct 2017 13:23:52 +0100 From: Hanno Böck <hanno@...eck.de> To: oss-security@...ts.openwall.com Subject: Fw: Security risk of vim swap files I just sent this to the vim dev list, but I guess it's interesting for oss-security, too. Begin forwarded message: Date: Tue, 31 Oct 2017 11:30:50 +0100 Subject: Security risk of vim swap files Hi, I wanted to point out an issue here with vim swap files that make them a security problem. By default vim creates a file with the name .filename.swp in the same directory while editing. They contain the full content of the edited file. This usually gets deleted upon exit, but not if vim crashes or gets killed (e.g. due to a reboot). On web servers this can be a severe security risk. One can e.g. scan for web hosts that have swap files of PHP configuration files and thus expose settings like database passwords. (e.g. wget http://example.com/.wp-config.php.swp ) In a scan of the alexa top 1 million I found ~750 instances of such files. I tried to inform affected people as best as I could. I also discovered such scans in my own web server logs, so I assume black hats are already aware of this and it's actively exploitet. I was wondering how to best avoid this on my own servers and I first thought about saving the swap files to tmp ( with "set directory"). However on multiuser systems this creates another security problem. These files are world readable, thus instead of leaking information to the world it's now leaking information to other users on the same system. Thus even if one is aware of the issue it's nontrivial to get secure settings (I've now worked around this by having per-user tmp dirs with secure permissions.) I think vim should change the behavior of swap files: 1. they should be stored in /tmp by default 2. they should have secure permissions (tmp file security is a tricky thing and needs careful consideration to avoid symlink attacks and the like, but there are dedicated functions for this like mkstemp). 3. Ideally they also shouldn't leak currently edited filenames (e.g. they shouldn't be called /tmp/.test.txt.swp, but more something like /tmp/.vim_swap.123782173) -- Hanno Böck https://hboeck.de/ mail/jabber: hanno@...eck.de GPG: FE73757FA60E4E21B937579FA5880072BBB51E42
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