CyberRota Analysis
AI-GeneratedUnbound versions 1.20.0 through 1.25.1 are vulnerable when configured with 'serve-expired: yes' and specific timeout settings that deviate from recommended values, leading to improper handling of aged client replies. This misconfiguration can allow a malicious actor to exploit the system, causing a degradation in resolution service by dropping new clients for duplicate queries when the reply address counter exceeds its limit. Organizations using Unbound with these configurations should prioritize addressing this vulnerability to ensure reliable DNS resolution and prevent potential service disruptions.
Public Exploit Signal
A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.
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Original NVD Description
In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the serve expired logic drops an aged client reply without performing the correct accounting for the number of reply addresses for the query. Other identical branches outside of serve expired perform the correct decrement. Since the counter is never decremented in such scenario, it can reach the maximum limit and new clients for duplicate in-flight queries are silently dropped resulting in degradation of resolution service. A malicious actor can exploit the vulnerability by querying the resolver for a client-controlled slow-on-demand authoritative zone that can drive the counter past the threshold. Shipped defaults for 'serve-expired-client-timeout: 1800' and 'discard-timeout: 1900' make the branch unreachable.
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