CVE-2026-47180 in Zeroconf
Summary
by MITRE • 07/17/2026
Zeroconf is a pure Python implementation of multicast DNS service discovery. Prior to 0.149.5, DNSIncoming._decode_labels_at_offset recurses once per DNS-name compression pointer, and a single mDNS packet carrying chained pointers can trigger a RecursionError that escapes DNSIncoming.__init__, causing sustained CPU burn, log flooding, and degraded mDNS-dependent features for unauthenticated hosts on the local link over UDP/5353 (224.0.0.251 / ff02::fb). This issue is fixed in version 0.149.5.
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Analysis
by VulDB Data Team • 07/17/2026
The vulnerability described represents a critical recursion flaw in the Zeroconf Python implementation that affects multicast DNS service discovery functionality. This issue manifests when processing specially crafted mDNS packets containing chained compression pointers, creating a recursive decoding scenario that can lead to system instability and denial of service conditions. The flaw specifically impacts DNSIncoming._decode_labels_at_offset method which processes DNS name decompression, where each pointer in the chain triggers another recursive call without proper bounds checking or depth limiting mechanisms.
The technical exploitation of this vulnerability occurs through the manipulation of DNS name compression pointers within mDNS packets transmitted over UDP port 5353 to the multicast address 224.0.0.251 or IPv6 equivalent ff02::fb. When a maliciously constructed packet contains multiple chained pointers, the recursive decoding function exhausts available stack space and triggers a RecursionError exception that escapes the DNSIncoming._init_ constructor. This recursive descent continues until the system's recursion limit is exceeded, causing the Python interpreter to terminate the execution thread or potentially crash the entire process handling mDNS traffic.
The operational impact of this vulnerability extends beyond simple service disruption to encompass sustained CPU utilization and log flooding that can degrade overall network performance for all devices on the local link. Unauthenticated hosts capable of sending UDP packets to the multicast address can trigger this condition repeatedly, leading to persistent resource exhaustion that affects critical mDNS-dependent services such as printer discovery, file sharing, and device enumeration across the network segment. The vulnerability affects systems where Zeroconf is deployed for service discovery without proper input validation or rate limiting mechanisms.
This vulnerability aligns with CWE-674: Uncontrolled Recursion, which specifically addresses situations where recursive functions lack proper termination conditions or depth limits, leading to stack overflow conditions. From an ATT&CK perspective, this represents a denial of service technique that leverages protocol implementation weaknesses in network services, specifically targeting the DNS resolution process within local network discovery mechanisms. The vulnerability demonstrates poor input validation and inadequate recursion depth management in network protocol parsing code.
The fix implemented in Zeroconf version 0.149.5 addresses this issue through enhanced recursion depth limiting and proper bounds checking within the DNS name decoding process. This mitigation strategy prevents excessive recursive calls by establishing maximum recursion limits or converting the recursive algorithm to an iterative approach that processes pointer chains without consuming stack space. Organizations should immediately upgrade to version 0.149.5 or later to protect against this vulnerability, while also implementing network-level monitoring for unusual mDNS traffic patterns that might indicate exploitation attempts.
Additional defensive measures include implementing rate limiting on mDNS packet processing, deploying network segmentation to isolate critical services from untrusted hosts, and configuring intrusion detection systems to monitor for malformed DNS packets containing chained pointers. The vulnerability highlights the importance of proper recursion handling in protocol implementations and demonstrates how seemingly benign network discovery mechanisms can become attack vectors when not properly secured against recursive input manipulation attacks.