Synology-SA-21:27 ISC BIND

Publish Time: 2021-11-01 18:33:53 UTC+8

Last Updated: 2022-11-09 18:09:45 UTC+8



A vulnerability allows remote attackers to conduct denial-of-service attacks via a susceptible version of Synology DNS Server.

Affected Products

Product Severity Fixed Release Availability
DNS Server for DSM 7.0 Moderate Upgrade to 9.16.23-6117 or above.
DNS Server for DSM 6.2 Moderate Will not fix
DNS Server for SRM 1.2 Moderate Will not fix


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  • CVE-2021-25219
    • Severity: Moderate
    • CVSS3 Base Score: 5.3
    • CVSS3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
    • 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.



Revision Date Description
1 2021-11-01 Initial public release.
2 2022-02-17 Update for DNS Server for DSM 7.0 is now available in Affected Products.