-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-19:12.telnet Security Advisory The FreeBSD Project Topic: telnet(1) client multiple vulnerabilities Category: contrib Module: contrib/telnet Announced: 2019-07-24 Credits: Juniper Networks Affects: All supported versions of FreeBSD. Corrected: 2019-07-19 15:37:29 UTC (stable/12, 12.0-STABLE) 2019-07-24 12:51:52 UTC (releng/12.0, 12.0-RELEASE-p8) 2019-07-19 15:27:53 UTC (stable/11, 11.2-STABLE) 2019-07-24 12:51:52 UTC (releng/11.2, 11.2-RELEASE-p12) 2019-07-24 12:51:52 UTC (releng/11.3, 11.3-RELEASE-p1) CVE Name: CVE-2019-0053 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit . I. Background The telnet(1) command is a TELNET protocol client, used primarily to establish terminal sessions across a network. II. Problem Description Insufficient validation of environment variables in the telnet client supplied in FreeBSD can lead to stack-based buffer overflows. A stack- based overflow is present in the handling of environment variables when connecting via the telnet client to remote telnet servers. This issue only affects the telnet client. Inbound telnet sessions to telnetd(8) are not affected by this issue. III. Impact These buffer overflows may be triggered when connecting to a malicious server, or by an active attacker in the network path between the client and server. Specially crafted TELNET command sequences may cause the execution of arbitrary code with the privileges of the user invoking telnet(1). IV. Workaround Do not use telnet(1) to connect to untrusted machines or over an untrusted network. V. Solution Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. 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 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-19:12/telnet.patch # fetch https://security.FreeBSD.org/patches/SA-19:12/telnet.patch.asc # gpg --verify telnet.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile the operating system using buildworld and installworld as described in . VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/12/ r350139 releng/12.0/ r350281 stable/11/ r350140 releng/11.2/ r350281 releng/11.3/ r350281 - ------------------------------------------------------------------------- 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/A6HiuWv54gCjWNV05eS9J6n5cIFAl04WltfFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEZD MEU4NzhBRTVBRkU3ODgwMjhENjM1NUQzOTc5MkY0OUVBN0U1QzIACgkQ05eS9J6n 5cLOzA//YxRZNUr+d8B+t6DnBUbVvthJiY9sQ1YPXUIJmp4QA7wvXr5UjURw+6qv raxEp6JmF06wZK4RjeIFckQD6s2wnjO5VHO80Zbs0nD4NejQGeDAIlVdKqofOtJv bBQNSY3vPAtumyfElc+N19rKetAjGbsUjOMbn87GlWrit4lqcavBQsdmSlQB5gVA dFAFsVxr+ujjATnrCmIpFiaDk0unyJ7Gtz7jiM9I8xZueJtM49/9kNCFFLKCMUl8 HpB2k0cb18GVNJoKtzo1nELOM/oIJVO5HZt1fmYG/RgeL1BSyzg4q/5jXJQopJ2h Qax7fmMP+RpGGrfp9Uom63tj79eQk2NirpUtfAaYkfGKzj6fNcq/7jxZfbobx0R8 uTiF88mlv2/SGxpo11Z/QBqOSYTQtjDRYJvjCo77g7YW8HauECC3tiklpPfFOIO8 m5qNOORKI74Do377GBF3gxDF2T8ILwj1j7nKHf3apotvQXJkkbpWBG7ADRTFcZWd PMKdYiDPHV33YmCAg9tOAqV4O7TvaB07ZLKiI6kuSBtPVrazB8Az/oRJwfF6JQ6g 4ZdinyCrXWYrWslkW8402GKCERFFYJUvwLSUqHxYMRgZWPy9zf/mH56vh4bleYnP kz2X7OgtB3Juu0Uzwv927+KZuyzitniaPlLe9tsyBwXFbUM+BrY= =LWVf -----END PGP SIGNATURE-----