oss-sec mailing list archives
Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack
From: Dan Rosenberg <dan.j.rosenberg () gmail com>
Date: Tue, 1 Mar 2011 07:19:10 -0500
Not sure it is fixable, or maybe using a lock on the symbolic link while fetching its target (to be tested to be sure that such locks cannot be overridden from shell).
The easiest way is to just open the target with the O_NOFOLLOW flag to avoid following symlinks and abort on failure. If you need to support systems that don't have this flag, then perhaps you could consider using an application-specific temporary directory instead of operating in the world-writable /tmp.
Also, I don't see a reason why a hard link couldn't be used for exploitation instead.Hard link are not detectable (lstat), they are treated like normal files.
Sure they are - just open the file, fstat() it, and check the st_nlink field. If it's more than one, you know there's hard linking going on. Sometimes this kind of check introduces a race condition of its own where the file can be removed by the attacker after a file descriptor is obtained but before the fstat(), but in this case since an attacker would be creating a hard link to a victim's file, he wouldn't be able to remove it since it's in a sticky-bit /tmp directory. -Dan
Current thread:
- CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Helgi Þormar Þorbjörnsson (Feb 28)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Dan Rosenberg (Feb 28)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Pierre Joye (Mar 01)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Helgi Þormar Þorbjörnsson (Mar 01)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Vincent Danen (Mar 03)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Dan Rosenberg (Mar 01)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Pierre Joye (Mar 01)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Helgi Þormar Þorbjörnsson (Mar 01)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Helgi Þormar Þorbjörnsson (Mar 08)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Vincent Danen (Mar 11)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Pierre Joye (Mar 01)
- Re: CVE Request: PEAR Installer 1.9.1 <= - Symlink Attack Dan Rosenberg (Feb 28)