A samba security update has been released for Debian GNU/Linux 9 LTS to address several vulnerabilities.

DLA 2668-1: samba security update

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Debian LTS Advisory DLA-2668-1 debian-lts@lists.debian.org
  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