Headline
CVE-2020-7454
In FreeBSD 12.1-STABLE before r360971, 12.1-RELEASE before p5, 11.4-STABLE before r360971, 11.4-BETA1 before p1 and 11.3-RELEASE before p9, libalias does not properly validate packet length resulting in modules causing an out of bounds read/write condition if no checking was built into the module.
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-20:12.libalias Security Advisory The FreeBSD Project Topic: Insufficient packet length validation in libalias Category: core Module: libalias Announced: 2020-05-12 Credits: Lucas Leong (@_wmliang_) of Trend Micro Zero Day Initiative Vishnu working with Trend Micro Zero Day Initiative Affects: All supported versions of FreeBSD. Corrected: 2020-05-12 16:49:04 UTC (stable/12, 12.1-STABLE) 2020-05-12 16:51:11 UTC (releng/12.1, 12.1-RELEASE-p5) 2020-05-12 16:49:04 UTC (stable/11, 11.4-STABLE) 2020-05-12 16:51:11 UTC (releng/11.4, 11.4-BETA1-p1) 2020-05-12 16:51:11 UTC (releng/11.3, 11.3-RELEASE-p9) CVE Name: CVE-2020-7454 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit . I. Background The ipfw(4) system facility allows IP packet filtering, redirecting, and traffic accounting. The ipfw(4) packet filter also contains two different methods of accomplishing network address translation (NAT): in-kernel and userspace. Both implementations use the same functions provided by libalias. The libalias(3) library is a collection of functions for aliasing and dealiasing of IP packets, intended for masquerading and NAT. Additionally, libalias(3) includes modules to support protocols that require additional logic to support address translation. Note: libalias(3) is not used by either the pf(4) or ipf(4) firewalls. II. Problem Description libalias(3) packet handlers do not properly validate the packet length before accessing the protocol headers. As a result, if a libalias(3) module does not properly validate the packet length before accessing the protocol header, it is possible for an out of bound read or write condition to occur. III. Impact A malicious attacker could send specially constructed packets that exploit the lack of validation allowing the attacker to read or write memory either from the kernel (for the in-kernel NAT implementation) or from the process space for natd (for the userspace implementation). IV. Workaround No workaround is available. Only systems using NAT and ipfw together are affected. Systems using ipfw(4) without NAT, or systems leveraging pf(4) or ipf(4) are not affected. V. Solution Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date, and reboot. Perform one of the following: 1) 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: # freebsd-update fetch # freebsd-update install # shutdown -r +10min “Rebooting for a security update” 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. # fetch https://security.FreeBSD.org/patches/SA-20:12/libalias.patch # fetch https://security.FreeBSD.org/patches/SA-20:12/libalias.patch.asc # gpg --verify libalias.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in and reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/12/ r360971 releng/12.1/ r360972 stable/11/ r360971 releng/11.4/ r360972 releng/11.3/ r360972 - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: VII. References The latest revision of this advisory is available at -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE/A6HiuWv54gCjWNV05eS9J6n5cIFAl663tdfFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEZD MEU4NzhBRTVBRkU3ODgwMjhENjM1NUQzOTc5MkY0OUVBN0U1QzIACgkQ05eS9J6n 5cK1Iw/7BpU400GeYsWt6xd+tUuBqGGB6a28+4G/e2GkqMF83vwAaf9+M4siM4Md t0RUDLhcC3irLtGehLcXmVdWZUakmacGa3pGza3E8qdCSQC6+VdO4ghzk5fRlVf0 jmcvCi7zml0YhmATkfMBscPeOJmvENUpouVIwzn4CXMwCKMofjKXdW8+tiT6ppsD RVVeUrGdslVo40KZ8wqxx4y2IMKZ7qW/UZnqWQFAAD3d3iQBJXORpy1xn0AZStY2 ddnhkKdBOyKs5JLoJfSwP8vyTi4iMXPFILP1spuTAqxEFBRTZ3rTE81jimznhp5N /OXI92khj6deiTc1kun+ef3n89e1w6KO4Dt1LUNL08N4mpEwLwvBGLS/5v/3KVpm Q6XknASLY4RaWdj1D5zbPY6F+JFUv22la5mdia4Gn1zxjsyZNMGgM6nx8OCZn4qg JTr7RT4f+EubkEwYD1sw60iTYsqM3o1gFUzkFdEAotWU4tl3nxRkUwusikX7Uu7e 2QY46Sg/6NxW+oelx1qDGjMlP2CIlEsEqj4ND3eJzJT6nef1xmmTUUu+kQF4TBtX J7XqmuTzST2ySPhBUEIOKbjmzdbe+zpbraADhq5BS3zKKmcVSqmqJxkXPxzCwIwb uMcg2spQ5fzP/BquOGdQSx0rD3dQ5lTNX6QZyDaKHZR78ZAEiVE= =I9Vz -----END PGP SIGNATURE-----