[SECURITY] [DLA 2668-1] samba security update

Debian LTS Advisory DLA-2668-1 [email protected]
https://www.debian.org/lts/security/ Abhijith PA
May 29, 2021 https://wiki.debian.org/LTS

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