CVE-2021-25216
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A second vulnerability in BIND's GSSAPI security policy negotiation can be targeted by a buffer overflow attack
rank 60 = 21 + 25 + 4 + 10 + 0
rank@v1 · this cycle
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.82367 · without this subject the record ranks 39
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 9.8, from NVD · without this subject the record ranks 35
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
rose on 2025-10-01 · without this subject the record ranks 56
How much of the world it touches
NVD CPE configurations
20 products in the CPE ranges · without this subject the record ranks 50
Someone else already set the date
CISA KEV remediation due date
no CISA due date · without this subject the record ranks 60
$4.11M = $4.99M incident cost x 1 exposure x 0.82367 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
This record is one instance of CWE-125, out-of-bounds read. The index holds 9767 prior instances of this class, 19 KEV-listed. The nearest of its KEV-listed records are drawn beside this. taxonomy@v1
Sources disagree here.
Both shown, dated. We don't pick winners. disagreement-rules@v1
Running ISC BIND9? Check your version
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Harm, if it fires from the vector and the weakness
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CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Nothing observed in held sources.
- RUNG 1Nothing observed in held sources
- RUNG 2Proof-of-concept published
- RUNG 3Exploited in the wild · CISA KEV listed
- RUNG 4Ransomware campaign use known
Affected & Fixed Versions as published
Show all 20 published ranges
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
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. receipt
Read the rest of the CNA's description
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.
NVD's analysis a second authority
- severity
- 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- weakness
- CWE-125
- affected versions
- debian linux 9.0; debian linux 10.0; isc bind >= 9.0.0 < 9.11.31; and 17 more, listed in full below
- also scored by
- [email protected] 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The CNA scored it 8.1 and NVD 9.8. Both are shown because both were published; we do not pick one.
check it yourself kb.isc.org openwall.com openwall.com openwall.com openwall.com debian.org +4 morereceipt
Dated events
Movement the material steps
This score more than doubled inside 72 hours. Both observations are in the full history below.
Show all 74 observations
74 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The full biography
Exploit probability more than doubled between 2025-04-13 and 2025-04-16 (0.05687 → 0.12537) and the record had been public for 5 years, 2 months when this index was last written.
The pattern, elsewhere
This record is one instance of CWE-125, out-of-bounds read. The index holds 9767 prior instances of this class, 19 KEV-listed. The nearest of its KEV-listed records are drawn beside this. [email protected]
"Matches n of m" counts the attributes the two records can both be compared on: the CVSS metrics they share a version of, any weakness class beyond this one, and the vendor. fit-rules@v1
9767 records in this class held. The six above are drawn from the ones CISA has listed as exploited, ranked by how much of the record matches this one. That is why every one of them is KEV-listed: the pool is, so the colour on those spokes says nothing the pool has not already said.
No curated product neighbourhood is held for this product, so the records above are the nearest this index can name. The neighbourhood table covers a small set of products and is extended by hand.
Siblings and hubs
Records related to this one
Its defect family
isc bind9
Of the 2 records in this family, this is the only one whose title names second bind gssapi.
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: held values
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Browse the index from here
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What usually comes next
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