CVE-2026-83813 is a vulnerability in the Twisted framework's DNS client UDP transport (twisted.names.dns.DNSDatagramProtocol) where DNS responses are accepted based only on matching transaction IDs without validating the source address. This allows an off-path attacker who can send UDP packets to the resolver's port to spoof DNS responses. The standard Twisted DNS client mitigates this by using per-query random source ports, increasing entropy, but the missing source address validation remains a weakness, especially for code using DNSDatagramProtocol directly. The CVSS score is low due to the attack complexity and limited impact.