Synology-SA-20:12 NXNSAttack

Publish Time: 2020-05-21 19:37:26 UTC+8

Last Updated: 2021-05-25 13:33:28 UTC+8



CVE-2020-8616 allows remote attackers to conduct denial-of-service attacks via a susceptible version of DNS Server.

None of Synology's products are affected as CVE-2020-12662 only affects when Unbound DNS resolver is enabled.

Affected Products

Product Severity Fixed Release Availability
DNS Server Important Upgrade to 2.2.2-5027 or above.
VPN Plus Server Not affected N/A




  • CVE-2020-8616

    • Severity: Important
    • CVSS3 Base Score: 8.6
    • CVSS3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:F/RL:O/RC:C
    • A malicious actor who intentionally exploits this lack of effective limitation on the number of fetches performed when processing referrals can, through the use of specially crafted referrals, cause a recursing server to issue a very large number of fetches in an attempt to process the referral. This has at least two potential effects: The performance of the recursing server can potentially be degraded by the additional work required to perform these fetches, and The attacker can exploit this behavior to use the recursing server as a reflector in a reflection attack with a high amplification factor.
  • CVE-2020-12662

    • Severity: Not affected
    • CVSS3 Base Score: 0.0
    • CVSS3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:N
    • Unbound before 1.10.1 has Insufficient Control of Network Message Volume, aka an "NXNSAttack" issue. This is triggered by random subdomains in the NSDNAME in NS records.



Revision Date Description
1 2020-05-21 Initial public release.
2 2020-12-08 Update for DNS Server is now available in Affected Products.