--- title: "CVE-2021-25216: A second vulnerability in BIND's GSSAPI… | CubePath" description: "In BIND 9.5.0 -> 9.11.29, 9.12.0 -> 9.16.13, and versions BIND 9.11.3-S1 -> 9.11.29-S1 and 9.16.8-S1 -> 9.16.13-S1 of BIND Supported Preview Edition…" language: en source: https://cubepath.com/security/cve/CVE-2021-25216 --- # CVE-2021-25216: A second vulnerability in BIND's GSSAPI… | CubePath ## Description In BIND 9.5.0 -> 9.11.29, 9.12.0 -> 9.16.13, and versions BIND 9.11.3-S1 -> 9.11.29-S1 and 9.16.8-S1 -> 9.16.13-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.1 of the BIND 9.17 development branch, 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 values for the tkey-gssapi-keytab or tkey-gssapi-credential configuration 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. For servers that meet these conditions, the ISC SPNEGO implementation is vulnerable to various attacks, depending on the CPU architecture for which BIND was built: For named binaries compiled for 64-bit platforms, this flaw can be used to trigger a buffer over-read, leading to a server crash. For named binaries compiled for 32-bit platforms, this flaw can be used to trigger a server crash due to a buffer overflow and possibly also to achieve remote code execution. We have determined that standard SPNEGO implementations are available in the MIT and Heimdal Kerberos libraries, which support a broad range of operating systems, rendering the ISC implementation unnecessary and obsolete. Therefore, to reduce the attack surface for BIND users, we will be removing the ISC SPNEGO implementation in the April releases of BIND 9.11 and 9.16 (it had already been dropped from BIND 9.17). We would not normally remove something from a stable ESV (Extended Support Version) of BIND, but since system libraries can replace the ISC SPNEGO implementation, we have made an exception in this case for reasons of stability and security. Official description from the CVE record, published by isc. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-25216) ## Key data ### CVSS 3.1 High 8.1 Score published by isc in the CVE record. CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H | Metric | Value | What it means | | ---------------------- | --------- | ----------------------------------------------------------------------------------------- | | Attack vector | Network | The vulnerable component can be reached over a network, possibly from the Internet. | | Attack complexity | High | The attack depends on conditions outside the attacker's control, so it takes preparation. | | Privileges required | None | No account or privileges are needed. | | User interaction | None | No action from any user is needed. | | Scope | Unchanged | The impact stays within the vulnerable component. | | Confidentiality impact | High | Serious or total effect on the secrecy of data. | | Integrity impact | High | Serious or total effect on the trustworthiness of data. | | Availability impact | High | Serious or total effect on availability. | CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at [first.org/cvss](https://www.first.org/cvss/) . ### EPSS Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days. Score 0.82992 (83.0% probability) Percentile 99.7% Scores of Nov 10, 2026 Model v2026.06.15 ## Affected products Products listed in the CVE record, as the CNA published them. - ISC BIND9 - affected: Open Source Branches 9.5 though 9.11 9.5.0 through versions before 9.11.31 - affected: Open Source Branches 9.12 though 9.16 9.12.0 through versions before 9.16.14 - affected: Supported Preview Branch 9.11-S 9.11.3-S1 through versions before 9.11.31-S1 - affected: Supported Preview Branch 9.16-S 9.16.8-S1 through versions before 9.16.14-S1 - affected: Development Branch 9.17 9.17.0 through versions before 9.17.2 ## References Links listed in the CVE record. They lead to other sites, which CubePath does not control. - [kb.isc.org/v1/docs/cve-2021-25215](https://kb.isc.org/v1/docs/cve-2021-25215) - [\[oss-security\] 20210428 ISC discloses three BIND vulnerabilities (CVE-2021-25214, CVE-2021-25215, and CVE-2021-25216)](http://www.openwall.com/lists/oss-security/2021/04/29/1) (openwall.com) mailing-list - [\[oss-security\] 20210429 Re: ISC discloses three BIND vulnerabilities (CVE-2021-25214, CVE-2021-25215, and CVE-2021-25216)](http://www.openwall.com/lists/oss-security/2021/04/29/2) (openwall.com) mailing-list - [\[oss-security\] 20210429 Re: ISC discloses three BIND vulnerabilities (CVE-2021-25214, CVE-2021-25215, and CVE-2021-25216)](http://www.openwall.com/lists/oss-security/2021/04/29/3) (openwall.com) mailing-list - [\[oss-security\] 20210429 Re: ISC discloses three BIND vulnerabilities (CVE-2021-25214, CVE-2021-25215, and CVE-2021-25216)](http://www.openwall.com/lists/oss-security/2021/04/29/4) (openwall.com) mailing-list - [DSA-4909](https://www.debian.org/security/2021/dsa-4909) (debian.org) vendor-advisory - [\[debian-lts-announce\] 20210504 \[SECURITY\] \[DLA 2647-1\] bind9 security update](https://lists.debian.org/debian-lts-announce/2021/05/msg00001.html) (lists.debian.org) mailing-list - [security.netapp.com/advisory/ntap-20210521-0006](https://security.netapp.com/advisory/ntap-20210521-0006/) - [zerodayinitiative.com/advisories/ZDI-21-657](https://www.zerodayinitiative.com/advisories/ZDI-21-657/) - [cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf](https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf) ## Timeline 1. ID reserved Jan 15, 2021 2. Record published Apr 29, 2021 3. Record last updated Sep 16, 2024 ## Look up another CVE ## About CubePath CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection. [Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection) Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 20:04 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)