From ciac@rumpole.llnl.gov Thu Sep 16 01:32:04 1999 From: CIAC Mail User Resent-From: mea culpa To: ciac-bulletin@rumpole.llnl.gov Resent-To: jericho@attrition.org Date: Tue, 14 Sep 1999 14:45:52 -0700 (PDT) Subject: CIAC Bulletin J-066: FreeBSD File Flags and Man-In-The-Middle Attack [ For Public Release ] -----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN FreeBSD File Flags and Man-In-The-Middle Attack September 7, 1999 17:00 GMT Number J-066 _____________________________________________________________________________ PROBLEM: A local user can execute a man-in-the-middle attack should certain programs fail when subsequent users sign on. PLATFORM: All systems running FreeBSD 3.2 (and earlier) or FreeBSD-Current before 1999/08/02. DAMAGE: A local user can snoop and alter all text that the other user (including root) writes. Results of this include the ability to execute commands as the user, and stealing the user's password (and anything else the user writes over the connection, including passwords for other machines). SOLUTION: Apply the available patches. There are no immediate or temporary workarounds. _____________________________________________________________________________ VULNERABILITY The risk is MEDIUM because the FreeBSD Advisory did not ASSESSMENT: indicate that this vulnerability had been discussed in public forums. _____________________________________________________________________________ [ Start FreeBSD Advisory ] ============================================================================= FreeBSD-SA-99:01 Security Advisory FreeBSD, Inc. Topic: BSD File Flags and Programming Techniques Category: core Module: kernel Announced: 1999-09-04 Affects: FreeBSD 3.2 (and earlier) FreeBSD-current before the correction date. Corrected: FreeBSD-3.3 RELEASE FreeBSD-current as of 1999/08/02 FreeBSD-3.2-stable as of 1999/08/02 FreeBSD-2.2.8-stable as of 1999/08/04 FreeBSD only: NO Patches: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-99:01/ I. Background BSD 4.4 added various flags to files in the file system. These flags control various aspects of which operations are permitted on those files. Historically, root has been been able to do all of these operations so many programs that knew they were running as root didn't check to make sure that these operations succeeded. II. Problem Description A user can set flags and mode on the device which they logged into. Since a bug in login and other similar programs causes the normal chown to fail, this first user will own the terminal of any login. III. Impact Local users can execute a man-in-the-middle attack against any other user (including root) when the other users logs in. This give them the ability to snoop and alter all text that the user writes. Results of this include the ability to execute commands as the user, and stealing the user's password (and anything else the users writes over the connection, including passwords for other machines). IV. Workaround None. V. Solution FreeBSD-current Index: kern/vfs_syscalls.c =================================================================== RCS file: /home/imp/FreeBSD/CVS/src/sys/kern/vfs_syscalls.c,v retrieving revision 1.125 retrieving revision 1.128 diff -u -r1.125 -r1.128 --- vfs_syscalls.c 1999/07/29 17:02:56 1.125 +++ vfs_syscalls.c 1999/08/04 04:52:18 1.128 @@ -1892,13 +1892,23 @@ int error; struct vattr vattr; + /* + * Prevent non-root users from setting flags on devices. When + * a device is reused, users can retain ownership of the device + * if they are allowed to set flags and programs assume that + * chown can't fail when done as root. + */ + if ((vp->v_type == VCHR || vp->v_type == VBLK) && + ((error = suser_xxx(p->p_ucred, p, PRISON_ROOT)) != 0)) + return (error); + VOP_LEASE(vp, p, p->p_ucred, LEASE_WRITE); vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p); VATTR_NULL(&vattr); vattr.va_flags = flags; error = VOP_SETATTR(vp, &vattr, p->p_ucred, p); VOP_UNLOCK(vp, 0, p); - return error; + return (error); } /* FreeBSD-3.2-stable Index: kern/vfs_syscalls.c =================================================================== RCS file: /home/imp/FreeBSD/CVS/src/sys/kern/vfs_syscalls.c,v retrieving revision 1.112.2.3 retrieving revision 1.112.2.5 diff -u -r1.112.2.3 -r1.112.2.5 --- vfs_syscalls.c 1999/07/30 01:07:23 1.112.2.3 +++ vfs_syscalls.c 1999/08/11 21:39:50 1.112.2.5 @@ -1839,13 +1839,23 @@ int error; struct vattr vattr; + /* + * Prevent non-root users from setting flags on devices. When + * a device is reused, users can retain ownership of the device + * if they are allowed to set flags and programs assume that + * chown can't fail when done as root. + */ + if ((vp->v_type == VCHR || vp->v_type == VBLK) && + ((error = suser(p->p_ucred, &p->p_acflag)) != 0)) + return (error); + VOP_LEASE(vp, p, p->p_ucred, LEASE_WRITE); vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p); VATTR_NULL(&vattr); vattr.va_flags = flags; error = VOP_SETATTR(vp, &vattr, p->p_ucred, p); VOP_UNLOCK(vp, 0, p); - return error; + return (error); } /* FreeBSD 2.2.8-stable: Index: kern/vfs_syscalls.c =================================================================== RCS file: /home/imp/FreeBSD/CVS/src/sys/kern/vfs_syscalls.c,v retrieving revision 1.51.2.7 retrieving revision 1.51.2.8 diff -u -r1.51.2.7 -r1.51.2.8 --- vfs_syscalls.c 1998/07/03 03:50:31 1.51.2.7 +++ vfs_syscalls.c 1999/08/04 18:58:56 1.51.2.8 @@ -1439,6 +1439,17 @@ if (error) return (error); vp = nd.ni_vp; + if ((error = VOP_GETATTR(vp, &vattr, p->p_ucred, p))) + return (error); + /* + * Prevent non-root users from setting flags on devices. When + * a device is reused, users can retain ownership of the device + * if they are allowed to set flags and programs assume that + * chown can't fail when done as root. + */ + if ((vp->v_type == VCHR || vp->v_type == VBLK) && + ((error = suser(p->p_ucred, &p->p_acflag)) != 0)) + return (error); LEASE_CHECK(vp, p, p->p_ucred, LEASE_WRITE); VOP_LOCK(vp); VATTR_NULL(&vattr); VI. Credits Theo de Raadt came up with the firewalling solution presented here. lumpy@blue.9mm.com brought this problem to light. ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: security-officer@freebsd.org Security notifications: security-notifications@freebsd.org Security public discussion: freebsd-security@freebsd.org PGP Key: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc Notice: Any patches in this document may not apply cleanly due to modifications caused by digital signature or mailer software. Please reference the URL listed at the top of this document for original copies of all patches if necessary. ============================================================================= [ End FreeBSD Advisory ] _____________________________________________________________________________ CIAC wishes to acknowledge the contributions of FreeBSD, Inc. for the information contained in this bulletin. _____________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), use one of the following methods to contact CIAC: 1. Call the CIAC voice number 925-422-8193 and leave a message, or 2. Call 888-449-8369 to send a Sky Page to the CIAC duty person or 3. Send e-mail to 4498369@skytel.com, or 4. Call 800-201-9288 for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ (or http://ciac.llnl.gov -- they're the same machine) Anonymous FTP: ftp.ciac.org (or ciac.llnl.gov -- they're the same machine) Modem access: +1 (925) 423-4753 (28.8K baud) +1 (925) 423-3331 (28.8K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. CIAC-BULLETIN for Advisories, highest priority - time critical information and Bulletins, important computer security information; 2. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 3. SPI-NOTES, for discussion of problems and solutions regarding the use of SPI products. Our mailing lists are managed by a public domain software package called Majordomo, which ignores E-mail header subject lines. To subscribe (add yourself) to one of our mailing lists, send the following request as the E-mail message body, substituting ciac-bulletin, spi-announce OR spi-notes for list-name: E-mail to ciac-listproc@llnl.gov or majordomo@rumpole.llnl.gov: subscribe list-name e.g., subscribe ciac-bulletin You will receive an acknowledgment email immediately with a confirmation that you will need to mail back to the addresses above, as per the instructions in the email. This is a partial protection to make sure you are really the one who asked to be signed up for the list in question. If you include the word 'help' in the body of an email to the above address, it will also send back an information file on how to subscribe/unsubscribe, get past issues of CIAC bulletins via email, etc. PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) J-056: Microsoft "Encapsulated SMTP Address" Vulnerability J-057: Windows NT(r) Terminal Servers DOS Vulnerability J-058: Microsoft "Malformed HTTP Request Header" Vulnerability J-059: IBM AIX (pdnsd) Buffer Overflow Vulnerability J-060: Microsoft Office "ODBC" Vulnerabilities J-061: Lotus Notes Domino Server Denial of Service Attacks J-062: Netscape Enterprise and FastTrack Web Servers Buffer Overflow J-063: Domain Name System (DNS) Denial of Service (DoS) Attacks J-064: ActiveX Controls, Scriptlet.typlib & Eyedog, Vulnerabilities J-065: Wu-ftpd Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBN9mLiLnzJzdsy3QZAQEdFwP+MQVtk6YrhBvNTnezANewu3A8Cplm7qmt UMFmmgXDxypS3fQCrE+PTIi36tCYtMOvNYXofUATjCht8J6JMFoiq5nMF5yniwL3 nfEWCisB7rN7sofxfINzgJ25UeriAZAVJ1D+LxOP9JHH9V9OiMyUypxkOgIch7gr LTkzIOhciMA= =T2RU -----END PGP SIGNATURE-----