CVE-2021-25216Network attack vector

Remote crash via SPNEGO out-of-bounds access

Published Apr 29, 2021 · Updated Sep 16, 2024

Buffer overflow in affected BIND 9 releases allows remote attackers to crash named via crafted GSS-TSIG negotiation. ISC has not published the parsing operation or input-length error within its SPNEGO implementation that produces the out-of-bounds access. Exploitation requires non-default GSS-TSIG settings; the 64-bit outcome is a crash, while 32-bit builds also expose code-execution risk.

CVSS severity8.1
High
EPSS probability82.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in affected BIND 9 releases allows remote attackers to crash named via crafted GSS-TSIG negotiation. ISC has not published the parsing operation or input-length error within its SPNEGO implementation that produces the out-of-bounds access. Exploitation requires non-default GSS-TSIG settings; the 64-bit outcome is a crash, while 32-bit builds also expose code-execution risk.

The record

CVE
CVE-2021-25216
Published
Apr 29, 2021
Updated
Sep 16, 2024
Vendor
Internet Systems Consortium
Product
BIND 9
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Development Branch 9.17 9.17.0 through versions before 9.17.2
  2. Affected versionversion=Open Source Branches 9.12 though 9.16 9.12.0 through versions before 9.16.14
  3. Affected versionversion=Open Source Branches 9.5 though 9.11 9.5.0 through versions before 9.11.31
  4. Affected versionversion=Supported Preview Branch 9.11-S 9.11.3-S1 through versions before 9.11.31-S1
  5. Affected versionversion=Supported Preview Branch 9.16-S 9.16.8-S1 through versions before 9.16.14-S1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Internet Systems Consortium · BIND 9version=Development Branch 9.17 9.17.0 through versions before 9.17.2; version=Open Source Branches 9.12 though 9.16 9.12.0 through versions before 9.16.14; version=Open Source Branches 9.5 though 9.11 9.5.0 through versions before 9.11.31; version=Supported Preview Branch 9.11-S 9.11.3-S1 through versions before 9.11.31-S1; version=Supported Preview Branch 9.16-S 9.16.8-S1 through versions before 9.16.14-S1

Published CVSS scores

9.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.4Internet Systems ConsortiumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
8.1Internet Systems ConsortiumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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