CVE-2020-8625: A vulnerability in BIND's GSSAPI security policy negotiation can be targeted by a buffer overflow attack

Michael McNally mcnally at isc.org
Wed Feb 17 20:01:13 UTC 2021


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-officer at isc.org. To report a new issue, please
encrypt your message using security-officer at 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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