CVE-2026-30872 in OpenWRT
Summary
by MITRE • 03/20/2026
OpenWrt Project is a Linux operating system targeting embedded devices. In versions prior to 24.10.6 and 25.12.1, the mdns daemon has a Stack-based Buffer Overflow vulnerability in the match_ipv6_addresses function, triggered when processing PTR queries for IPv6 reverse DNS domains (.ip6.arpa) received via multicast DNS on UDP port 5353. During processing, the domain name from name_buffer is copied via strcpy into a fixed 256-byte stack buffer, and then the reverse IPv6 request is extracted into a buffer of only 46 bytes (INET6_ADDRSTRLEN). Because the length of the data is never validated before this extraction, an attacker can supply input larger than 46 bytes, causing an out-of-bounds write. This allows a specially crafted DNS query to overflow the stack buffer in match_ipv6_addresses, potentially enabling remote code execution. This issue has been fixed in versions 24.10.6 and 25.12.1.
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Analysis
by VulDB Data Team • 03/24/2026
The vulnerability identified as CVE-2026-30872 affects the OpenWrt Project's mdns daemon, which serves as a critical component in embedded networking environments where multicast DNS functionality is essential for device discovery and name resolution. This issue resides within the match_ipv6_addresses function, a specialized handler for processing IPv6 reverse DNS queries within the .ip6.arpa domain space. The daemon operates on UDP port 5353, the standard multicast DNS port, making it susceptible to attacks targeting this common network service. The vulnerability stems from inadequate input validation during DNS query processing, specifically when handling PTR records that map IPv6 addresses to domain names, creating a dangerous scenario where user-supplied data directly influences buffer operations without proper boundary checks.
The technical flaw manifests through a classic stack-based buffer overflow condition that occurs when the mdns daemon processes incoming multicast DNS queries. During normal operation, the daemon receives a domain name in name_buffer that is copied using strcpy into a fixed 256-byte stack buffer without any length verification. Subsequently, the daemon attempts to extract the reverse IPv6 address into a destination buffer of only 46 bytes, which is insufficient for handling the full range of valid IPv6 address representations. This mismatch between source data size and destination buffer capacity creates a scenario where maliciously crafted DNS queries containing oversized IPv6 address data can overflow the stack buffer. The vulnerability is particularly dangerous because it operates within the daemon's core processing loop, meaning that any valid multicast DNS query can potentially trigger this condition, regardless of whether it originates from a legitimate source or an attacker.
The operational impact of this vulnerability extends beyond simple buffer corruption, as the stack-based overflow creates potential for remote code execution within the mdns daemon process. Attackers can craft DNS queries with oversized IPv6 address data that exceeds the 46-byte destination buffer, causing memory corruption that may allow arbitrary code execution with the privileges of the mdns daemon. This represents a significant security risk in embedded environments where OpenWrt devices often serve as network gateways, routers, or IoT devices with limited security controls. The vulnerability affects all versions prior to 24.10.6 and 25.12.1, meaning that a substantial portion of deployed OpenWrt systems remain at risk. The attack vector requires only the ability to send multicast DNS queries to the target device on UDP port 5353, making it particularly dangerous in local network environments where such traffic is common.
The root cause of this vulnerability aligns with CWE-121 Stack-based Buffer Overflow, a well-documented weakness in software security that has been addressed through numerous industry standards and best practices. This vulnerability also maps to ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, as the exploitation would likely involve crafting malicious DNS queries that leverage the daemon's processing capabilities to execute arbitrary code. The fix implemented in versions 24.10.6 and 25.12.1 addresses the core issue by introducing proper bounds checking and input validation before buffer operations. Security practitioners should prioritize patching affected systems, as the vulnerability chain requires minimal prerequisites for exploitation and could enable attackers to gain persistent access to network infrastructure. Organizations deploying OpenWrt systems should conduct thorough vulnerability assessments to identify all affected devices and implement monitoring for suspicious multicast DNS traffic patterns that might indicate exploitation attempts. The remediation approach demonstrates the importance of input validation and proper buffer management in network services, particularly those operating in embedded environments where resource constraints may limit defensive capabilities.