CVE: CVE-2020-8625
Document version: 2.0
Posting date: 17 February 2021
Program impacted: BIND
Versions affected: BIND 9.5.0 -> 9.11.27, 9.12.0 -> 9.16.11, and versions
BIND 9.11.3-S1 -> 9.11.27-S1 and 9.16.8-S1 -> 9.16.11-S1
of BIND Supported Preview Edition. Also release versions
9.17.0 -> 9.17.1 of the BIND 9.17 development branch
Severity: High
Exploitable: Remotely
Description:
GSS-TSIG is an extension to the TSIG protocol which is intended
to support the secure exchange of keys for use in verifying the
authenticity of communications between parties on a network.
SPNEGO is a negotiation mechanism used by GSSAPI, the application
protocol interface for GSS-TSIG.
The SPNEGO implementation used by BIND has been found to be
vulnerable to a buffer overflow attack.
Impact:
BIND servers are vulnerable if they are running an affected
version and are configured to use GSS-TSIG features.
In a configuration which uses BIND's default settings the
vulnerable code path is NOT exposed, but a server can be rendered
vulnerable by explicitly setting valid values for the
tkey-gssapi-keytab or tkey-gssapi-credentialconfiguration options.
Although the default configuration is not vulnerable, GSS-TSIG
is frequently used in networks where BIND is integrated with
Samba, as well as in mixed-server environments that combine BIND
servers with Active Directory domain controllers.
The most likely outcome of a successful exploitation of the
vulnerability is a crash of the named process. However, remote
code execution, while unproven, is theoretically possible.
CVSS Score: 8.1
CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score, please visit:
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H&version=3.1.
Workarounds:
This vulnerability only affects servers configured to use GSS-TSIG,
most often to sign dynamic updates. If another mechanism can be
used to authenticate updates, the vulnerability can be avoided
by choosing not to enable the use of GSS-TSIG features.
On some platforms it may be possible to build a working BIND
installation that is not vulnerable to CVE-2020-8625 by providing
the --disable-isc-spnego command-line argument when running the
./configure script in the top level of the BIND source directory,
before compiling and linking named.
Choosing to configure and build BIND without the ISC SPNEGO
implementation does not produce a vulnerable BIND on any platform,
but on platforms where GSSAPI support in the system is lacking,
building without the ISC SPNEGO implementation may result in
unusable GSSAPI features (such as an inability to use GSS-TSIG-signed
DDNS updates).
Active exploits:
We are not aware of any active exploits.
Solution:
Upgrade to the patched release most closely related to your current version
of BIND:
+ BIND 9.11.28
+ BIND 9.16.12
BIND Supported Preview Edition is a special feature-preview branch of BIND provided to
eligible ISC support customers.
+ BIND 9.11.28-S1
+ BIND 9.16.12-S1
Acknowledgments:
ISC would like to thank an anonymous party, working in conjunction
with Trend Micro Zero Day Initiative, for reporting this issue to us.
Document revision history:
1.0 Early Notification, 9 February 2021
2.0 Public Disclosure, 17 February 2021
Related documents:
See our BIND 9 Security Vulnerability Matrix for a complete
listing of security vulnerabilities and versions affected.
Do you still have questions? Questions regarding this advisory
should go to security-offi...@isc.org. To report a new issue, please
encrypt your message using security-offi...@isc.org's PGP key which
can be found here: https://www.isc.org/pgpkey/. If you are unable
to use encrypted email, you may also report new issues at:
https://www.isc.org/reportbug/.
Note:
ISC patches only currently supported versions. When possible we
indicate EOL versions affected. (For current information on which
versions are actively supported, please see
https://www.isc.org/download/.)
ISC Security Vulnerability Disclosure Policy:
Details of our current security advisory policy and practice can
be found in the ISC Software Defect and Security Vulnerability
Disclosure Policy at https://kb.isc.org/docs/aa-00861.
The Knowledgebase article https://kb.isc.org/docs/cve-2020-8625 is
the complete and official security advisory document.
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