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6 <title>Samba - Security Announcement Archive</title>
11 <H2>CVE-2021-23192.html:</H2>
15 ====================================================================
16 == Subject: Subsequent DCE/RPC fragment injection vulnerability
18 == CVE ID#: CVE-2021-23192
20 == Versions: Samba 4.10.0 and later.
22 == Summary: If a client to a Samba server sent a very large
23 DCE/RPC request, and chose to fragment it, an
24 attacker could replace later fragments with
25 their own data, bypassing the signature requirements.
26 =====================================================================
32 Samba implements DCE/RPC, and in most cases it is provided over and
33 protected by the underlying SMB transport, with protections like 'SMB
36 However there are other cases where large DCE/RPC request payloads are exchanged
37 and fragmented into several pieces. If this happens over untrusted transports
38 (e.g. directly over TCP/IP or anonymous SMB) clients will typically
39 protect by an explicit authentication at the DCE/RPC layer, e.g. with
40 GSSAPI/Kerberos/NTLMSSP or Netlogon Secure Channel.
42 Because the checks on the fragment protection were not done between
43 the policy controls on the header and the subsequent fragments, an attacker
44 could replace subsequent fragments in requests with their own data, which
45 might be able to alter the server behaviour.
47 DCE/RPC is a core component of all Samba servers, but we are most
48 concerned about Samba as a Domain Controller, given the role as a
49 centrally trusted service.
51 As active directory domain controller this issue affects Samba versions greater
54 As NT4 classic domain controller, domain member or standalone server
55 this issue affects Samba versions greater or equal to 4.13.0.
61 Patches addressing both these issues have been posted to:
63 https://www.samba.org/samba/security/
65 Additionally, Samba 4.15.2, 4.14.10 and 4.13.14 have been issued
66 as security releases to correct the defect. Samba administrators are
67 advised to upgrade to these releases or apply the patch as soon
74 CVSS:3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N (4.8)
80 Setting "dcesrv:max auth states=0" in the smb.conf will provide
81 some mitigation against this issue.
83 There are no known problems with this change as
84 NT4 classic domain controller, domain member or standalone server.
86 But it disables "Security Context Multiplexing" and may reopen
87 https://bugzilla.samba.org/show_bug.cgi?id=11892.
88 which means domain members running things like Cisco ISE or
89 VMWare View may no longer work. This applies only to
90 active directory domain controllers.
96 Originally reported by Stefan Metzmacher of SerNet
98 Patches provided by Stefan Metzmacher of SerNet and the Samba Team.
99 Advisory by Andrew Bartlett of Catalyst and the Samba Team.
101 ==========================================================
102 == Our Code, Our Bugs, Our Responsibility.
104 ==========================================================