In NLnet Labs Unbound up to and including version 1.25.1, when unwanted-reply-threshold is enabled (set to any value greater than zero), glue records of 0.0.0.0/::0 can short-circuit Unbound, on systems that can direct such traffic, by issuing DNS queries and receiving seemingly unwanted replies since the remote IP does not match the original source IP of 0.0.0.0/::0. This behavior keeps on looping for the glue records and pushing the counter to the configured unwanted-reply-threshold that triggers a defensive cache clear. A malicious actor who controls a delegation that returns in-bailiwick glue of 0.0.0.0/::0 can drive the counter to the limit of unwanted-reply-threshold to the threshold and trigger a cache clean of the message and rrset caches; at will, indefinitely, without sending a single spoofed packet. The iterator uses the 0.0.0.0/::0 glue, and a system that can route this (e.g., Linux kernel routes the datagram over loopback), Unbounds own listener answers from 127.0.0.1. Because of the mismatch of 0.0.0.0 and 127.0.0.1, in this example, Unbound accounts the reply as an unwanted (probably spoofed) answer. The counter resets to zero on every cache flush, so the attack loops forever.
Weakness
The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Unbound | Ubuntu | upstream | * |
Potential Mitigations
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/120.html
- https://cwe.mitre.org/data/definitions/15.html
- https://cwe.mitre.org/data/definitions/182.html
- https://cwe.mitre.org/data/definitions/3.html
- https://cwe.mitre.org/data/definitions/43.html
- https://cwe.mitre.org/data/definitions/6.html
- https://cwe.mitre.org/data/definitions/71.html
- https://cwe.mitre.org/data/definitions/73.html
- https://cwe.mitre.org/data/definitions/85.html