Executive brief
PowerDNS DNSdist, a load balancer for DNS traffic, contains a security flaw in its DNS over HTTPS (DoH) component. When a specific security setting is manually disabled, the system fails to check access control lists (ACLs), allowing unauthorized users to send queries that should have been blocked. This could allow attackers to bypass network restrictions and use the DNS service without permission.
Technical details
An incorrect authorization vulnerability (CWE-863) exists in PowerDNS DNSdist when using the nghttp2 provider for DNS over HTTPS (DoH) frontends. If the 'early_acl_drop' (earlyACLDrop in Lua) configuration option is explicitly disabled (it is enabled by default), the engine skips the ACL check entirely. This allows any remote client to successfully send DoH queries regardless of the configured access restrictions. The vulnerability affects versions 1.9.0 through 1.9.11 and 2.0.0 through 2.0.2. A fix is available 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
- 2026-02-12: disclosed: Discovery date
- 2026-03-31: advisory: Vendor advisory published
- 2026-03-31: patched: Fixed versions 1.9.12 and 2.0.3 released