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ASB-2016.0028 - [UNIX/Linux] Samba: Multiple vulnerabilities

Date: 10 March 2016
References: ESB-2016.0672  ESB-2016.0697  ESB-2016.0764  ESB-2016.0814  ESB-2016.1832  

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===========================================================================
                         AUSCERT Security Bulletin

                               ASB-2016.0028
          Multiple vulnerabilities have been identified in Samba
                               10 March 2016

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:              Samba
Operating System:     UNIX variants (UNIX, Linux, OSX)
Impact/Access:        Overwrite Arbitrary Files -- Existing Account      
                      Denial of Service         -- Remote/Unauthenticated
                      Access Confidential Data  -- Remote/Unauthenticated
                      Reduced Security          -- Existing Account      
Resolution:           Patch/Upgrade
CVE Names:            CVE-2016-0771 CVE-2015-7560 
Member content until: Saturday, April  9 2016

OVERVIEW

        Multiple vulnerabilities have been identified in Samba prior to 
        security releases 4.4.0rc4, 4.3.6, 4.2.9 and 4.1.23. [1,2]


IMPACT

        The vendor has provided the following details regarding the 
        vulnerabilities:
        
        CVE-2016-0771: "All versions of Samba from 4.0.0 to 4.4.0rc3 
        inclusive, when deployed as an AD DC and choose to run the internal
        DNS server, are vulnerable to an out-of-bounds read issue during DNS
        TXT record handling caused by users with permission to modify DNS 
        records.
        
        A malicious client can upload a specially constructed DNS TXT 
        record, resulting in a remote denial-of-service attack. As long as 
        the affected TXT record remains undisturbed in the Samba database, a
        targeted DNS query may continue to trigger this exploit.
        
        While unlikely, the out-of-bounds read may bypass safety checks and
        allow leakage of memory from the server in the form of a DNS TXT 
        reply.
        
        By default only authenticated accounts can upload DNS records, as 
        "allow dns updates = secure only" is the default. Any other value 
        would allow anonymous clients to trigger this bug, which is a much 
        higher risk." [1]
        
        CVE-2015-7560: "All versions of Samba from 3.2.0 to 4.4.0rc3 
        inclusive are vulnerable to a malicious client overwriting the 
        ownership of ACLs using symlinks. An authenticated malicious client
        can use SMB1 UNIX extensions to create a symlink to a file or 
        directory, and then use non-UNIX SMB1 calls to overwrite the 
        contents of the ACL on the file or directory linked to." [2]


MITIGATION

        The vendor advises users to upgrade or patch as soon as possible to
        address these issues. [1,2]


REFERENCES

        [1] Out-of-bounds read in internal DNS server
            https://www.samba.org/samba/security/CVE-2016-0771.html

        [2] Incorrect ACL get/set allowed on symlink path.
            https://www.samba.org/samba/security/CVE-2015-7560.html

AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
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).
                On call after hours for member emergencies only.
===========================================================================
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