CVE-2021-25219 | Lame cache can be abused to severely degrade resolver performance

In BIND 9.3.0 -> 9.11.35, 9.12.0 -> 9.16.21, and versions 9.9.3-S1 -> 9.11.35-S1 and 9.16.8-S1 -> 9.16.21-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.18 of the BIND 9.17 development branch, exploitation of broken authoritative servers using a flaw in response processing can cause degradation in BIND resolver performance. The way the lame cache is currently designed makes it possible for its internal data structures to grow almost infinitely, which may cause significant delays in client query processing.

Published: 2021-10-27 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-25219 is rated Moderate Risk (49.2/100): CVSS Medium severity, with high exploitation likelihood (EPSS 8.00%, 94th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-25219

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-23 12.90% 8.00% -4.90%
2 2026-06-15 0.96% 12.90% +11.94%
3 2026-03-20 — 0.96% —

Full EPSS history (31 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-25219

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-25219

OS Trackers for CVE-2021-25219

vendor priority summary link
alpine medium CVE-2021-25219: 1 source package rows (bind); 97 state rows across 9 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 89. https://security.alpinelinux.org/vuln/CVE-2021-25219
debian not yet assigned CVE-2021-25219 not yet assigned priority: Debian including 1 source packages (bind9), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-25219
gentoo low CVE-2021-25219: 1 GLSA(s) (202210-25), 2 atom(s) (net-dns/bind, net-dns/bind-tools); latest impact low. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-25219
redhat medium — https://access.redhat.com/security/cve/CVE-2021-25219
suse medium CVE-2021-25219 severity moderate: SUSE including 388 source package names (amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, amazon/suse-sles-15-sp1-chost-byos-v20220127-hvm-ssd-x86_64, …), 1447 product×package rows across 201 product lines (HPE Helion OpenStack 8, Image SLES12-SP5-Azure-BYOS, … (201 product lines)): Fixed 1033, Known Not Affected 362, Known Affected 52. https://www.suse.com/security/cve/CVE-2021-25219/
ubuntu medium CVE-2021-25219 medium priority: Ubuntu including 1 source packages (bind9), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): released 7, needs-triage 1. https://ubuntu.com/security/CVE-2021-25219

Affected software / configurations for CVE-2021-25219

Vendor Product Version Raw CPE
isc bind >= 9.3.0, < 9.11.36 cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
isc bind >= 9.12.0, < 9.16.22 cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
isc bind >= 9.17.0, < 9.17.19 cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
isc bind 9.9.3 cpe:2.3:a:isc:bind:9.9.3:s1:*:*:supported_preview:*:*:*
isc bind 9.9.12 cpe:2.3:a:isc:bind:9.9.12:s1:*:*:supported_preview:*:*:*
isc bind 9.9.13 cpe:2.3:a:isc:bind:9.9.13:s1:*:*:supported_preview:*:*:*
isc bind 9.10.5 cpe:2.3:a:isc:bind:9.10.5:s1:*:*:supported_preview:*:*:*
isc bind 9.10.7 cpe:2.3:a:isc:bind:9.10.7:s1:*:*:supported_preview:*:*:*
isc bind 9.11.3 cpe:2.3:a:isc:bind:9.11.3:s1:*:*:supported_preview:*:*:*
isc bind 9.11.5 cpe:2.3:a:isc:bind:9.11.5:s3:*:*:supported_preview:*:*:*
isc bind 9.11.5 cpe:2.3:a:isc:bind:9.11.5:s5:*:*:supported_preview:*:*:*
isc bind 9.11.5 cpe:2.3:a:isc:bind:9.11.5:s6:*:*:supported_preview:*:*:*
isc bind 9.11.6 cpe:2.3:a:isc:bind:9.11.6:s1:*:*:supported_preview:*:*:*
isc bind 9.11.7 cpe:2.3:a:isc:bind:9.11.7:s1:*:*:supported_preview:*:*:*
isc bind 9.11.8 cpe:2.3:a:isc:bind:9.11.8:s1:*:*:supported_preview:*:*:*
isc bind 9.11.12 cpe:2.3:a:isc:bind:9.11.12:s1:*:*:supported_preview:*:*:*
isc bind 9.11.21 cpe:2.3:a:isc:bind:9.11.21:s1:*:*:supported_preview:*:*:*
isc bind 9.11.27 cpe:2.3:a:isc:bind:9.11.27:s1:*:*:supported_preview:*:*:*
isc bind 9.11.29 cpe:2.3:a:isc:bind:9.11.29:s1:*:*:supported_preview:*:*:*
isc bind 9.11.35 cpe:2.3:a:isc:bind:9.11.35:s1:*:*:supported_preview:*:*:*
isc bind 9.16.8 cpe:2.3:a:isc:bind:9.16.8:s1:*:*:supported_preview:*:*:*
isc bind 9.16.11 cpe:2.3:a:isc:bind:9.16.11:s1:*:*:supported_preview:*:*:*
isc bind 9.16.13 cpe:2.3:a:isc:bind:9.16.13:s1:*:*:supported_preview:*:*:*
isc bind 9.16.21 cpe:2.3:a:isc:bind:9.16.21:s1:*:*:supported_preview:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
netapp h300s_firmware — cpe:2.3:o:netapp:h300s_firmware:-:*:*:*:*:*:*:*
netapp h500s_firmware — cpe:2.3:o:netapp:h500s_firmware:-:*:*:*:*:*:*:*
netapp h700s_firmware — cpe:2.3:o:netapp:h700s_firmware:-:*:*:*:*:*:*:*
netapp h300e_firmware — cpe:2.3:o:netapp:h300e_firmware:-:*:*:*:*:*:*:*
netapp h500e_firmware — cpe:2.3:o:netapp:h500e_firmware:-:*:*:*:*:*:*:*
netapp h700e_firmware — cpe:2.3:o:netapp:h700e_firmware:-:*:*:*:*:*:*:*
netapp h410s_firmware — cpe:2.3:o:netapp:h410s_firmware:-:*:*:*:*:*:*:*
netapp h410c_firmware — cpe:2.3:o:netapp:h410c_firmware:-:*:*:*:*:*:*:*
netapp cloud_backup — cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*
siemens sinec_infrastructure_network_services < 1.0.1.1 cpe:2.3:a:siemens:sinec_infrastructure_network_services:*:*:*:*:*:*:*:*
oracle http_server 12.2.1.3.0 cpe:2.3:a:oracle:http_server:12.2.1.3.0:*:*:*:*:*:*:*
oracle http_server 12.2.1.4.0 cpe:2.3:a:oracle:http_server:12.2.1.4.0:*:*:*:*:*:*:*
oracle zfs_storage_appliance_kit 8.8 cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*

References for CVE-2021-25219

URL Tags
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf Patch Third Party Advisory
https://kb.isc.org/v1/docs/cve-2021-25219 Vendor Advisory
https://lists.debian.org/debian-lts-announce/2021/11/msg00001.html Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EF4NAVRV4H3W4GA3LGGZYUKD3HSJBAVW/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YGV7SA27CTYLGFJSPUM3V36ZWK7WWDI4/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YTKC4E3HUOLYN5IA4EBL4VAQSWG2ZVTX/
https://security.gentoo.org/glsa/202210-25 Third Party Advisory
https://security.netapp.com/advisory/ntap-20211118-0002/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4994 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Third Party Advisory
cvelogic Threat Intelligence