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NVD / CVE Program· CNA isc

CVE-2021-25216: A second vulnerability in BIND's GSSAPI security policy negotiation can be targeted by a buffer overflow attack

CriticalCVSS 9.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: This week (action score 64/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 82.9% (FIRST EPSS); higher than 99.6% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: bind (Alpine:v3.10) 9.16.15-r0; bind9 (Debian:10) 1:9.11.5.P4+dfsg-5.1+deb10u5; bind9 (Debian:12) 1:9.16.15-1.
  • Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Don’t wait for the next maintenance window. Upgrade to bind (Alpine:v3.10) 9.16.15-r0; bind9 (Debian:10) 1:9.11.5.P4+dfsg-5.1+deb10u5; bind9 (Debian:12) 1:9.16.15-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

Published
Apr 28, 2021
Updated
Jun 16, 2026
EPSS
82.9% · 99th percentile

Report tools

JSON

Action score

64

This week

Don’t wait for the next maintenance window.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
25 / 30 · 82.9%

CNA vs NVD score

NVD
9.8
CNA · isc
8.1
1.7 point gap

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Follow CVE-2021-25216

When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
debiandebian linux
iscbind
siemenssinec infrastructure network services
netappactive iq unified manager
netappcloud backup
netappaff a250 firmware
netappaff a250
netappaff 500f firmware
netappaff 500f
netapph300s firmware
netapph300s
netapph500s firmware

and 11 more

Versions reported by the vendor

Affected version ranges reported by the assigning authority (isc). Independent of NVD's CPE analysis and usually ahead of it.

  • ISC BIND9

    • Open Source Branches 9.5 though 9.11 9.5.0 through versions before 9.11.31, Open Source Branches 9.12 though 9.16 9.12.0 through versions before 9.16.14, Supported Preview Branch 9.11-S 9.11.3-S1 through versions before 9.11.31-S1, Supported Preview Branch 9.16-S 9.16.8-S1 through versions before 9.16.14-S1, Development Branch 9.17 9.17.0 through versions before 9.17.2affected
Affected versions · NVD (20)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux10.0
  • debian debian linux9.0
  • isc bind9.17.0 and later · before 9.17.12
  • isc bind9.0.0 and later · before 9.11.31
  • isc bind9.12.0 and later · before 9.16.15
  • isc bind9.10.5
  • isc bind9.10.7
  • isc bind9.11.12
  • isc bind9.11.21
  • isc bind9.11.27
  • isc bind9.11.29
  • isc bind9.11.3
  • isc bind9.11.5
  • isc bind9.11.6
  • isc bind9.11.7
  • isc bind9.11.8
  • isc bind9.16.11
  • isc bind9.16.13
  • isc bind9.16.8
  • isc bind9.9.12

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Alpine:v3.10bindfrom 9.0.0 · before 9.16.15-r09.16.15-r0
Debian:10bind9before 1:9.11.5.P4+dfsg-5.1+deb10u51:9.11.5.P4+dfsg-5.1+deb10u5
Debian:12bind9before 1:9.16.15-11:9.16.15-1
Debian:9bind9before 1:9.10.3.dfsg.P4-12.3+deb9u91:9.10.3.dfsg.P4-12.3+deb9u9
SUSE:HPE Helion OpenStack 8bindbefore 9.9.9P1-63.25.19.9.9P1-63.25.1
SUSE:Linux Enterprise Point of Sale 11 SP3bindbefore 9.9.6P1-0.51.26.19.9.6P1-0.51.26.1

Same product

debian: all records

Other highest-scoring records for the same primary product.

  • CVE-2016-9079A use-after-free vulnerability in SVG Animation has been discovered.KEV
    86Now
  • CVE-2024-44308The issue was addressed with improved checks.KEV
    68This week
  • CVE-2024-44309A cookie management issue was addressed with improved state management.KEV
    62This week

Published before and after this one in the same product

  • ← EarlierCVE-2018-5735Oct 30, 2019 · Backport of the fix for CVE-2017-3137 leads to assertion failure in validator.c:1858
    30Monitor
  • ← EarlierCVE-2021-25215Apr 28, 2021 · An assertion check can fail while answering queries for DNAME records that require the DNAME to be processed to resolve itself
    34Monitor
  • Later →CVE-2015-1877Jun 2, 2021 · The open_generic_xdg_mime function in xdg-open in xdg-utils 1.1.0 rc1 in Debian, when using dash, does not properly handle local variables…
    36Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
alpine:bind9.16.15-r0 · Alpine:v3.10Package registry (OSV)
debian:bind91:9.16.15-1 · Debian:12Package registry (OSV)
suse:bind9.9.9P1-63.25.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Not on record for this CVE: EPSS history · patch commit or PR link · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-125 · Out-of-bounds Read

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (9 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records