Executive brief
PowerDNS DNSdist, a load balancer for DNS traffic, is vulnerable to a flaw that can cause the service to crash. An attacker can send specially crafted DNS responses that, when processed by custom scripts, cause the system to attempt to write data outside of its allocated memory. This results in a denial of service, preventing the system from handling legitimate DNS traffic for users and applications.
Technical details
An out-of-bounds write vulnerability (CWE-787) exists in PowerDNS DNSdist when custom Lua code utilizes the DNSQuestion:changeName or DNSResponse:changeName methods. The flaw is triggered when a rewritten DNS packet becomes larger than the initial response and exceeds the 65535-byte limit, causing the DNS packet writer (dnswriter.cc) to write beyond allocated buffers. This is reachable via the network by sending crafted DNS responses to a DNSdist instance configured with these specific Lua methods. The primary impact is a process crash resulting in a denial of service. The issue is fixed in versions 1.9.12 and 2.0.3.
Affected products
- PowerDNS DNSdist 1.9.0 to 1.9.11, 2.0.0 to 2.0.2
Timeline
- 2026-03-04: disclosed: Discovery date
- 2026-03-31: advisory: Vendor advisory published
- 2026-03-31: patched: Fixed versions 1.9.12 and 2.0.3 released