Lior Shafir

**Name of the Vulnerable Software and Affected Versions** PowerDNS Recursor versions 4.1.0 through 4.3.0 **Description** The issue in the DNS protocol allows malicious parties to use recursive DNS services to attack third-party authoritative name servers, resulting in degraded performance. This is triggered by random subdomains in the NSDNAME in NS records. The attack uses a crafted reply by an authoritative name server to amplify the resulting traffic between the recursive and other authoritative name servers. **Recommendations** For PowerDNS Recursor versions 4.1.0 through 4.1.15, consider updating to version 4.1.16 to mitigate the impact of this issue. For PowerDNS Recursor versions 4.2.0 through 4.2.1, consider updating to version 4.2.2 to mitigate the impact of this issue. For PowerDNS Recursor versions 4.3.0, consider updating to version 4.3.1 to mitigate the impact of this issue.

**Name of the Vulnerable Software and Affected Versions** Unbound versions prior to 1.10.1 **Description** The issue is related to Insufficient Control of Network Message Volume, also known as an "NXNSAttack" issue. This is triggered by random subdomains in the NSDNAME in NS records. **Recommendations** For versions prior to 1.10.1, update to version 1.10.1 or later to resolve the issue.

**Name of the Vulnerable Software and Affected Versions** BIND versions prior to the fixed version Windows DNS Server (affected versions not specified) PowerDNS Recursor (affected versions not specified) **Description** The issue is related to a lack of effective limitation on the number of fetches performed when processing referrals, which can cause a recursing server to issue a large number of fetches. This can lead to degradation of the server's performance and potentially be exploited in a reflection attack with a high amplification factor. The vulnerability can be exploited by a remote attacker to trigger an assertion failure in tsig.c, causing a denial of service. **Recommendations** For BIND, update to a version that includes the fix for this issue. For Windows DNS Server, apply the mitigation measures proposed by the vendor, as described in the security advisory ADV200009. For PowerDNS Recursor, follow the guidance provided in the security advisory PowerDNS Advisory 2020-01. As a temporary workaround, consider restricting the number of fetches performed when processing referrals to minimize the risk of exploitation. Restrict access to the vulnerable `tsig.c` function to prevent assertion failures until a patch is available. At the moment, there is no information about a newer version that contains a fix for this vulnerability for some of the affected software.