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============================================================================= FreeBSD-SA-13:06.mmap Security Advisory The FreeBSD Project
Topic: Privilege escalation via mmap
Category: core Module: kernel Announced: 2013-06-18 Credits: Konstantin Belousov Alan Cox Affects: FreeBSD 9.0 and later Corrected: 2013-06-18 07:04:19 UTC (stable/9, 9.1-STABLE) 2013-06-18 07:05:51 UTC (releng/9.1, 9.1-RELEASE-p4) CVE Name: CVE-2013-2171
For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:http://security.FreeBSD.org/>.
v1.0 2013-06-18 Initial release. v1.1 2013-06-21 Corrected correction date. Added workaround information.
The FreeBSD virtual memory system allows files to be memory-mapped. All or parts of a file can be made available to a process via its address space. The process can then access the file using memory operations rather than filesystem I/O calls.
The ptrace(2) system call provides tracing and debugging facilities by allowing one process (the tracing process) to watch and control another (the traced process).
II. Problem Description
Due to insufficient permission checks in the virtual memory system, a tracing process (such as a debugger) may be able to modify portions of the traced process's address space to which the traced process itself does not have write access.
This error can be exploited to allow unauthorized modification of an arbitrary file to which the attacker has read access, but not write access. Depending on the file and the nature of the modifications, this can result in privilege escalation.
To exploit this vulnerability, an attacker must be able to run arbitrary code with user privileges on the target system.
Systems that do not allow unprivileged users to use the ptrace(2) system call are not vulnerable, this can be accomplished by setting the sysctl variable security.bsd.unprivileged_proc_debug to zero. Please note that this will also prevent debugging tools, for instance gdb, truss, procstat, as well as some built-in debugging facilities in certain scripting language like PHP, etc., from working for unprivileged users.
The following command will set the sysctl accordingly and works until the next reboot of the system:
To make this change persistent across reboot, the system administrator should also add the setting into /etc/sysctl.conf:
echo 'security.bsd.unprivileged_proc_debug=0' >> /etc/sysctl.conf
Perform one of the following:
1) Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date.
2) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility.
b) Apply the patch.
c) Recompile your kernel as described in <URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the system.
3) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility:
VI. Correction details
The following list contains the correction revision numbers for each affected branch.
stable/9/ r251902 releng/9.1/ r251903
To see which files were modified by a particular revision, run the following command, replacing XXXXXX with the revision number, on a machine with Subversion installed:
Or visit the following URL, replacing XXXXXX with the revision number:
The latest revision of this advisory is available at <URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-13:06.mmap.asc> -----BEGIN PGP SIGNATURE-----
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