|Reported by:||Douglas R. Reno||Owned by:||Douglas R. Reno|
New security release.
Release Announcements --------------------- These are a security releases in order to address the following defect: o CVE-2019-10197: Combination of parameters and permissions can allow user to escape from the share path definition. ======= Details ======= o CVE-2019-10197: Under certain parameter configurations, when an SMB client accesses a network share and the user does not have permission to access the share root directory, it is possible for the user to escape from the share to see the complete '/' filesystem. Unix permission checks in the kernel are still enforced. Changes: -------- o Jeremy Allison <firstname.lastname@example.org> * BUG 14035: CVE-2019-10197: Permissions check deny can allow user to escape from the share. o Stefan Metzmacher <email@example.com> * BUG 14035: CVE-2019-10197: Permissions check deny can allow user to escape from the share.
CVE-2019-10197.html ============================================================================== == Subject: Combination of parameters and permissions can allow user == to escape from the share path definition. == == CVE ID#: CVE-2019-10197 == == Versions: All versions of Samba from 4.9.0 onwards. == == Summary: Under certain parameter configurations, when an SMB == client accesses a network share and the user does not == have permission to access the share root directory, == it is possible for the user to escape from the share == to see the complete '/' filesystem. Unix permission == checks in the kernel are still enforced. == ============================================================================== =========== Description =========== On a Samba SMB server for all versions of Samba from 4.9.0 clients are able to escape outside the share root directory if certain configuration parameters set in the smb.conf file. The problem is reproducable if the 'wide links' option is explicitly set to 'yes' and either 'unix extensions = no' or 'allow insecure wide links = yes' is set in addition. If a client has no permissions to enter the share root directory it will get ACCESS_DENIED on the first request. However smbd has a cache that remembers if it successfully changed to a directory. This cache was not being reset on failure. The following SMB request will then silently operate in the wrong directory instead of returning ACCESS_DENIED. That directory is either the share root directory of a different share the client was operating on successfully before or the global root directory ('/') of the system. The unix token (uid, gid, list of groups) is always correctly impersonated before each operation, so the client is still restricted by the unix permissions enfored by the kernel. ================== Patch Availability ================== A patch addressing this defect has been posted to: https://www.samba.org/samba/security/ Additionally, Samba 4.9.13, 4.10.8 and 4.11.0rc3 have been issued as security releases to correct the defect. Patches against older Samba versions may be available at https://samba.org/samba/patches/. Samba vendors and administrators running affected versions are advised to upgrade or apply the patch as soon as possible. ================== CVSSv3 calculation ================== CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:H/RL:O/RC:C (8.7) ========== Workaround ========== The following methods can be used as a mitigation (only one is needed): - Use the 'sharesec' tool to configure a security descriptor for the share that's at least as strict as the permissions on the share root directory. - Use the 'valid users' option to allow only users/groups which are able to enter the share root directory. - Remove 'wide links = yes' if it's not really needed. - In some situations it might be an option to use 'chmod a+x' on the share root directory, but you need to make sure that files and subdirectories are protected by stricter permissions. You may also want to 'chmod a-w' in order to prevent new top level files and directories, which may have less restrictive permissions. ======= Credits ======= This problem was found by Stefan Metzmacher of SerNet and the Samba Team. Patches provided by Ralph BÃ¶hme and Stefan Metzmacher of SerNet and the Samba Team together with Jeremy Allison of Google and the Samba Team. ========================================================== == Our Code, Our Bugs, Our Responsibility. == The Samba Team ==========================================================
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