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-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2001.287 -- FreeBSD-SA-01:42.signal signal handling during exec may allow local root compromise 12 July 2001 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: kernel Vendor: FreeBSD Operating System: FreeBSD 4.X Impact: Root Compromise Access Required: Existing Account - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-01:42 Security Advisory FreeBSD, Inc. Topic: signal handling during exec may allow local root compromise Category: core Module: kernel Announced: 2001-07-10 Credits: Georgi Guninski <firstname.lastname@example.org> Affects: All released versions of FreeBSD 4.x, FreeBSD 4.3-STABLE prior to the correction date. Corrected: 2001-07-09 FreeBSD only: Yes I. Background When a process forks, it inherits the parent's signals. When the process execs, the kernel clears the signal handlers because they are not valid in the new address space. II. Problem Description A flaw exists in FreeBSD signal handler clearing that would allow for some signal handlers to remain in effect after the exec. Most of the signals were cleared, but some signal hanlders were not. This allowed an attacker to execute arbitrary code in the context of a setuid binary. All versions of 4.x prior to the correction date including and 4.3-RELEASE are vulnerable to this problem. The problem has been corrected by copying the inherited signal handlers and resetting the signals instead of sharing the signal handlers. III. Impact Local users may be able to gain increased privileges on the local system. IV. Workaround Do not allow untrusted users to gain access to the local system. V. Solution One of the following: 1) Upgrade your vulnerable FreeBSD system to 4.3-STABLE after the correction date. 2) To patch your present system: download the relevant patch from the below location, and execute the following commands as root: [FreeBSD 4.1, 4.2, and 4.3 base systems] This patch has been verified to apply to FreeBSD 4.1, 4.2, and 4.3 only. It may or may not apply to older releases. # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:42/signal-4.3.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:42/signal-4.3.patch.asc Verify the detached PGP signature using your PGP utility. # cd /usr/src/sys/kern # patch -p < /path/to/patch [ Recompile your kernel as described in http://www.freebsd.org/handbook/kernelconfig.html and reboot the system ] - -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (FreeBSD) Comment: FreeBSD: The Power To Serve iQCVAwUBO0sNtlUuHi5z0oilAQH3aAP/dXzWd8u8Ya9pwOB9ymK3fNQD4GqHaT1b vKthgZNumVcnoNL3LC/iuMlmufIuVdVXM12ISad+aW5HkqZ0tDFSc4GLA9cX/riN r66h7IBAOc0p+NQH8TTSjCehUC1Np40hgsca+/onIfhhV7MKGWDY6I6BwJF9UWvD ZY62Dx/1yI8= =gDIP - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/Information/advisories.html If you believe that your system has been compromised, contact AusCERT or your representative in FIRST (Forum of Incident Response and Security Teams). Internet Email: firstname.lastname@example.org Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). 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