============================================================================= AA-95.06 AUSCERT Advisory 15 June, 1995 S/Key Vulnerability in Logdaemon and FreeBSD ----------------------------------------------------------------------------- AUSCERT has received the following advice from Wietse Venema concerning a vulnerability in the S/Key implementation found in Logdaemon and FreeBSD. Users of these packages are strongly advised to take remedial action as soon as possible. Please contact Wietse Venema if you have any questions or need further information. Topic: Logdaemon/FreeBSD vulnerability in S/Key Source: Wietse Venema (wietse@wzv.win.tue.nl) ========================FORWARDED TEXT STARTS HERE============================ A vulnerability exists in my own S/Key software enhancements. Since these enhancements are in wide-spread use, a public announcement is appropriate. The vulnerability affects the following products: FreeBSD version 1.1.5.1 FreeBSD version 2.0 logdaemon versions before 4.9 I recommend that users of this software follow the instructions given below in section III. ----------------------------------------------------------------------------- I. Description An obscure oversight was found in software that I derived from the S/Key software from Bellcore (Bell Communications Research). Analysis revealed that my oversight introduces a vulnerability. Note: the vulnerability is not present in the original S/Key software from Bellcore. II. Impact Unauthorized users can gain privileges of other users, possibly including root. The vulnerability can be exploited only by users with a valid account. It cannot be exploited by arbitrary remote users. The vulnerability can affect all FreeBSD 1.1.5.1 and FreeBSD 2.0 implementations and all Logdaemon versions before 4.9. The problem exists only when S/Key logins are supported (which is the default for FreeBSD). Sites with S/Key logins disabled are not vulnerable. III. Solution Logdaemon users: ================ Upgrade to version 4.9 URL ftp://ftp.win.tue.nl/pub/security/logdaemon-4.9.tar.gz. MD5 checksum 3d01ecc63f621f962a0965f13fe57ca6 To plug the hole, build and install the ftpd, rexecd and login programs. If you installed the keysu and skeysh commands, these need to be replaced too. FreeBSD 1.1.5.1 and FreeBSD 2.0 users: ====================================== Retrieve the corrected files that match the system you are running: URL ftp://ftp.cdrom.com/pub/FreeBSD/CERT/libskey-1.1.5.1.tgz MD5 checksum bf3a8e8e10d63da9de550b0332107302 URL ftp://ftp.cdrom.com/pub/FreeBSD/CERT/libskey-2.0.tgz MD5 checksum d58a17f4216c3ee9b9831dbfcff93d29 Unpack the tar archive and follow the instructions in the README file. FreeBSD current users: ====================== Update your /usr/src/lib/libskey sources and rebuild and install libskey (both shared and non-shared versions). The vulnerability has been fixed with FreeBSD 2.0.5. ----------------------------------------------------------------------------- S/KEY is a trademark of Bellcore (Bell Communications Research). Wietse Venema appreciates helpful assistance with the resolution of this vulnerability from CERT/CC; Rodney W. Grimes, FreeBSD Core Team Member; Guido van Rooij, Philips Communication and Processing Services; Walter Belgers. =========================FORWARDED TEXT ENDS HERE============================= ---------------------------------------------------------------------------- If you believe that your system has been compromised, contact AUSCERT or your representative in FIRST (Forum of Incident Response and Security Teams). AUSCERT is the Australian Computer Emergency Response Team, funded by the Australian Academic Research Network (AARNet) for its members. It is located at The University of Queensland within the Prentice Centre. AUSCERT is a full member of the Forum of Incident Response and Security Teams (FIRST). AUSCERT maintains an anonymous FTP service which is found on: ftp://ftp.auscert.org.au. This archive contains past SERT and AUSCERT Advisories, and other computer security information. AUSCERT also maintains a World Wide Web service which is found on: http://www.auscert.org.au. Internet Email: auscert@auscert.org.au Facsimile: (07) 365 4477 Telephone: (07) 365 4417 (International: +61 7 365 4417) AUSCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for emergencies. Postal: Australian Computer Emergency Response Team c/- Prentice Centre The University of Queensland Brisbane Qld. 4072. AUSTRALIA