# CVE-2021-25216: A second vulnerability in BIND's GSSAPI security policy negotiation can be targeted by a buffer overflow attack > Attackers can cause crashes or execute code on BIND servers using GSS-TSIG via a buffer overflow in the SPNEGO implementation. - **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 29 Apr 2021 - **Updated:** 16 Sep 2024 - **Also known as:** ALPINE-CVE-2021-25216, DEBIAN-CVE-2021-25216, GHSA-4vh7-r4m9-4w3v, UBUNTU-CVE-2021-25216 ## What is CVE-2021-25216? CVE-2021-25216 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 29 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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. Weakness: CWE-125 (Out-of-bounds Read) ## Which versions are affected by CVE-2021-25216? It affects 14 products. Products: Debian Debian Linux, Isc Bind, Netapp Active Iq Unified Manager, Netapp Aff 500f Firmware, Netapp Aff A250 Firmware, Netapp Cloud Backup, Netapp H300e Firmware, Netapp H300s Firmware, Netapp H410s Firmware, Netapp H500e Firmware, Netapp H500s Firmware, Netapp H700e Firmware, Netapp H700s Firmware, Siemens Sinec Infrastructure Network Services. ## How do I fix CVE-2021-25216? Upgrade to a fixed version. ## Is CVE-2021-25216 being exploited? There is no known exploitation of CVE-2021-25216 in the wild and no public exploit code. ## Other vulnerabilities in Debian Debian Linux - [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild) - [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild) - [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild) - [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild) - [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-25216 and fix it if it is affected. What it is: CVE-2021-25216 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 29 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-25216 in the wild and no public exploit code. Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-25216/ (Markdown: https://insights.sbomify.com/CVE-2021-25216/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-25216 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-25216 - OSV: https://osv.dev/vulnerability/CVE-2021-25216 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-25216/ Summaries are generated and may contain mistakes; the official description above is the record.