FreeBSD Core Dump Symbolic Link Arbitrary File Modification
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Loss of Integrity
FreeBSD contains a flaw that may allow a malicious user to gain access to unauthorized privileges. The issue is triggered when the kernel follows a maliciously created symbolic link during its creation of core files using periodic(3), allowing arbitrary file modification. This flaw may lead to a loss of integrity.
Upgrade to corrected versions 3.2-STABLE or 3.3-RELEASE or higher, as it has been reported to fix this vulnerability. Also, FreeBSD has released a patch. It is also possible to correct the flaw by implementing the following workaround: disable periodic() core dumps by changing core size to zero.
# mv /usr/sbin/periodic /usr/sbin/periodic.bin
# cat > /usr/sbin/periodic
ulimit -c 0
# chmod 555 /usr/sbin/periodic