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Debian LTS Advisory DLA-2668-1                [email protected]
https://www.debian.org/lts/security/                          Abhijith PA
May 29, 2021                                  https://wiki.debian.org/LTS
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Package        : samba
Version        : 2:4.5.16+dfsg-1+deb9u4
CVE ID         : CVE-2019-10218 CVE-2019-14833 CVE-2019-14847 CVE-2019-14861 
                 CVE-2019-14870 CVE-2019-14902 CVE-2019-14907 CVE-2021-20254
Debian Bug     : 946786 

Several vulnerabilities were discovered in Samba, SMB/CIFS file, 
print, and login server for Unix


CVE-2019-10218

    A flaw was found in the samba client, where a malicious server can 
    supply a pathname to the client with separators. This could allow 
    the client to access files and folders outside of the SMB network 
    pathnames. An attacker could use this vulnerability to create 
    files outside of the current working directory using the 
    privileges of the client user.

CVE-2019-14833

    A flaw was found in Samba, in the way it handles a user password 
    change or a new password for a samba user. The Samba Active 
    Directory Domain Controller can be configured to use a custom 
    script to check for password complexity. This configuration can 
    fail to verify password complexity when non-ASCII characters are 
    used in the password, which could lead to weak passwords being set 
    for samba users, making it vulnerable to dictionary attacks.

CVE-2019-14847

    A flaw was found in samba where an attacker can crash AD DC LDAP 
    server via dirsync resulting in denial of service. Privilege 
    escalation is not possible with this issue.

CVE-2019-14861

    Samba have an issue, where the (poorly named) dnsserver RPC pipe 
    provides administrative facilities to modify DNS records and 
    zones. Samba, when acting as an AD DC, stores DNS records in LDAP. 
    In AD, the default permissions on the DNS partition allow creation 
    of new records by authenticated users. This is used for example to 
    allow machines to self-register in DNS. If a DNS record was 
    created that case-insensitively matched the name of the zone, the 
    ldb_qsort() and dns_name_compare() routines could be confused into 
    reading memory prior to the list of DNS entries when responding to 
    DnssrvEnumRecords() or DnssrvEnumRecords2() and so following 
    invalid memory as a pointer.

CVE-2019-14870

    Samba have an issue, where the S4U (MS-SFU) Kerberos delegation 
    model includes a feature allowing for a subset of clients to be 
    opted out of constrained delegation in any way, either S4U2Self or 
    regular Kerberos authentication, by forcing all tickets for these 
    clients to be non-forwardable. In AD this is implemented by a user 
    attribute delegation_not_allowed (aka not-delegated), which 
    translates to disallow-forwardable. However the Samba AD DC does 
    not do that for S4U2Self and does set the forwardable flag even if 
    the impersonated client has the not-delegated flag set.

CVE-2019-14902

    There is an issue in samba, where the removal of the right to 
    create or modify a subtree would not automatically be taken away 
    on all domain controllers.

CVE-2019-14907

    samba have an issue where if it is set with "log level = 3" (or 
    above) then the string obtained from the client, after a failed 
    character conversion, is printed. Such strings can be provided 
    during the NTLMSSP authentication exchange. In the Samba AD DC in 
    particular, this may cause a long-lived process(such as the RPC 
    server) to terminate. (In the file server case, the most likely 
    target, smbd, operates as process-per-client and so a crash there is harmless).

CVE-2021-20254

    A flaw was found in samba. The Samba smbd file server must map 
    Windows group identities (SIDs) into unix group ids (gids). The 
    code that performs this had a flaw that could allow it to read 
    data beyond the end of the array in the case where a negative 
    cache entry had been added to the mapping cache. This could cause 
    the calling code to return those values into the process token 
    that stores the group membership for a user. The highest threat 
    from this vulnerability is to data confidentiality and integrity.

For Debian 9 stretch, these problems have been fixed in version
2:4.5.16+dfsg-1+deb9u4.

We recommend that you upgrade your samba packages.

For the detailed security status of samba please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/samba

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS