Security Bugs in Kernel and Rsync

Nov 30, 2007

Security researchers at Secunia have reported two security bugs in the Rsync synchronization tool and one in the current Linux kernel.

All current versions of Rsync are affected by the bug according to the developers. The first vulnerability affects configurations in which the Rsync daemon runs with the "use chroot = no" option set. This gives attackers the ability to set up symlinks outside of the module’s hierarchy and thus gain write access to system components to work around security settings.

The second vulnerability is due to an error in the "exclude", "exclude from" and "filter" options which also allow attackers avoid security limits with symlinks, but with the restriction here that the attacker needs to know the name of the file to attack. The Rsync team’s security advisory contains more details.

The kernel vulnerability affects the ISDN subsystem in the current 2.6.23 version, and possibly older versions. A boundary error in the "isdn_net_setcfg()" function can cause a buffer overflow. The affected file is "drivers/isdn/i4l/isdn_net.c". To exploit the vulnerability, an attacker would need to address a carefully crafted IOCTL request to the "/dev/isdnctrl" pseudo device, and this assumes write privileges for the device. For more details on the bug and the affected file, see Bugreport 9416.

Secunia says that all three bugs are moderately critical. Whereas the Rsync developers have already released a patch that closes both gaps, the error in the kernel’s ISDN subsystem still exists. However, patches have been sent to the maintainers in question the bug report states. Rsync users are advised to read the updated rsyncd.conf manpage, expecially the "munge symlinks" section, in addition to applying the patch.

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