CVE-2021-25220

CVE-2021-25220 is a medium-severity vulnerability in Isc Bind with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-444.

Key facts

• Severity: Medium (CVSS 3.x base score 6.8)
• CVSS v2: 4.0
• EPSS exploit prediction: 3% (87th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-444
• Affected product: Isc Bind
• Published: 2022-03-23
• Last modified: 2026-06-17

Description

BIND 9.11.0 -> 9.11.36 9.12.0 -> 9.16.26 9.17.0 -> 9.18.0 BIND Supported Preview Editions: 9.11.4-S1 -> 9.11.36-S1 9.16.8-S1 -> 9.16.26-S1 Versions of BIND 9 earlier than those shown - back to 9.1.0, including Supported Preview Editions - are also believed to be affected but have not been tested as they are EOL. The cache could become poisoned with incorrect records leading to queries being made to the wrong servers, which might also result in false information being returned to clients.

Frequently asked questions

What is CVE-2021-25220?

BIND 9.11.0 -> 9.11.36 9.12.0 -> 9.16.26 9.17.0 -> 9.18.0 BIND Supported Preview Editions: 9.11.4-S1 -> 9.11.36-S1 9.16.8-S1 -> 9.16.26-S1 Versions of BIND 9 earlier than those shown - back to 9.1.0, including Supported Preview Editions - are also believed to be affected but have not been tested as they are EOL. The cache could become poisoned with incorrect records leading to queries being made to the wrong servers, which might also result in false information being returned to clients.

How severe is CVE-2021-25220?

CVE-2021-25220 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-25220 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (87th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-25220?

CVE-2021-25220 primarily affects Isc Bind. In total, 127 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-25220?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-25220 published?

CVE-2021-25220 was published on 2022-03-23 and last updated on 2026-06-17.

References

• https://cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf
• https://kb.isc.org/v1/docs/cve-2021-25220
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2SXT7247QTKNBQ67MNRGZD23ADXU6E5U/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5VX3I2U3ICOIEI5Y7OYA6CHOLFMNH3YQ/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/API7U5E7SX7BAAVFNW366FFJGD6NZZKV/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DE3UAVCPUMAKG27ZL5YXSP2C3RIOW3JZ/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NYD7US4HZRFUGAJ66ZTHFBYVP5N3OQBY/
• https://security.gentoo.org/glsa/202210-25
• https://security.netapp.com/advisory/ntap-20220408-0001/
• https://supportportal.juniper.net/s/article/2022-10-Security-Bulletin-Junos-OS-SRX-Series-Cache-poisoning-vulnerability-in-BIND-used-by-DNS-Proxy-CVE-2021-25220?language=en_US

Affected products (127)

• cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
• cpe:2.3:a:isc:bind:*:*:*:*:supported_preview:*:*:*
• cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:36:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h300s_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h500s_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h700s_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h300e_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h500e_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h700e_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h410s_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:netapp:h410c_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:a:siemens:sinec_ins:*:*:*:*:*:*:*:*
• cpe:2.3:a:siemens:sinec_ins:1.0:-:*:*:*:*:*:*
• cpe:2.3:a:siemens:sinec_ins:1.0:sp1:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:-:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r1-s1:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s1:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s2:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s3:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s4:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s5:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s6:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r2-s7:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3-s1:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3-s2:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3-s3:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3-s4:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3-s5:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.3:r3-s6:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.4:-:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.4:r1:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.4:r1-s1:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.4:r1-s2:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.4:r1-s3:*:*:*:*:*:*
• cpe:2.3:o:juniper:junos:19.4:r1-s4:*:*:*:*:*:*

More vulnerabilities in Isc Bind

• CVE-2008-0122 — Critical (CVSS 10.0): Off-by-one error in the inet_network function in libbind in ISC BIND 9.4.2 and earlier, as used in libc in FreeBSD 6.2…
• CVE-2001-0011 — Critical (CVSS 10.0): Buffer overflow in nslookupComplain function in BIND 4 allows remote attackers to gain root privileges.
• CVE-2001-0013 — Critical (CVSS 10.0): Format string vulnerability in nslookupComplain function in BIND 4 allows remote attackers to gain root privileges.
• CVE-2001-0010 — Critical (CVSS 10.0): Buffer overflow in transaction signature (TSIG) handling code in BIND 8 allows remote attackers to gain root privileges.
• CVE-2000-1029 — Critical (CVSS 10.0): Buffer overflow in host command allows a remote attacker to execute arbitrary commands via a long response to an AXFR…
• CVE-1999-0837 — Critical (CVSS 10.0): Denial of service in BIND by improperly closing TCP sessions via so_linger.

All CVEs affecting Isc Bind →

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• CVE-2025-55315 — Critical (CVSS 9.9): Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an authorized…
• CVE-2020-15049 — Critical (CVSS 9.9): An issue was discovered in http/ContentLengthInterpreter.cc in Squid before 4.12 and 5.x before 5.0.3. A Request…
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