CVE-2026-24401 in Avahi
Summary
by MITRE • 01/24/2026
Avahi is a system which facilitates service discovery on a local network via the mDNS/DNS-SD protocol suite. In versions 0.9rc2 and below, avahi-daemon can be crashed via a segmentation fault by sending an unsolicited mDNS response containing a recursive CNAME record, where the alias and canonical name point to the same domain (e.g., "h.local" as a CNAME for "h.local"). This causes unbounded recursion in the lookup_handle_cname function, leading to stack exhaustion. The vulnerability affects record browsers where AVAHI_LOOKUP_USE_MULTICAST is set explicitly, which includes record browsers created by resolvers used by nss-mdns. This issue is patched in commit 78eab31128479f06e30beb8c1cbf99dd921e2524.
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Analysis
by VulDB Data Team • 02/12/2026
The vulnerability identified as CVE-2026-24401 resides within the Avahi service discovery system, which operates on local networks using the mDNS/DNS-SD protocol suite to enable automatic service discovery. This particular flaw manifests in versions 0.9rc2 and earlier, where the avahi-daemon process becomes susceptible to a segmentation fault when processing unsolicited mDNS responses containing recursive CNAME records. The specific condition triggering this vulnerability occurs when a CNAME record references itself, creating a scenario where "h.local" serves as both an alias and canonical name for the same domain. This self-referential CNAME record creates an infinite loop within the lookup_handle_cname function, resulting in unbounded recursion that ultimately exhausts the stack space allocated to the daemon process.
The technical exploitation of this vulnerability leverages the mDNS protocol's handling of CNAME records within the context of multicast DNS lookups, specifically affecting implementations that utilize the AVAHI_LOOKUP_USE_MULTICAST flag. This flag is explicitly set in record browsers created by nss-mdns resolvers, making the affected system components particularly vulnerable to this recursive lookup behavior. The flaw represents a classic stack overflow vulnerability that stems from inadequate input validation and lack of recursion depth limiting within the DNS record processing logic. From a cybersecurity perspective, this vulnerability aligns with CWE-674, which describes "Uncontrolled Recursion" and falls under the broader category of software defects that can lead to denial of service conditions through resource exhaustion. The vulnerability's impact extends beyond simple daemon crashes as it can be exploited by remote attackers to disrupt local network services, potentially affecting the availability of network discovery services that many applications depend upon for proper operation.
The operational impact of this vulnerability creates significant disruption in local network environments where Avahi services are deployed, particularly in enterprise and home network scenarios where automatic service discovery is relied upon for device connectivity and resource sharing. When exploited, the segmentation fault causes the avahi-daemon to terminate unexpectedly, leading to a complete disruption of service discovery functionality on the affected network segment. This can result in users experiencing difficulties connecting to network services, printers, file shares, and other discoverable resources that depend on mDNS for their operation. Network administrators may find their systems temporarily unavailable for service discovery operations, potentially affecting the usability of applications that utilize nss-mdns for hostname resolution. The vulnerability's exploitation does not require authentication or special privileges, making it particularly dangerous as it can be triggered by any entity capable of sending mDNS packets to the network, including malicious actors or compromised devices within the local network. The patch referenced in commit 78eab31128479f06e30beb8c1cbf99dd921e2524 addresses this issue by implementing proper recursion detection and limiting mechanisms within the CNAME lookup processing, preventing the unbounded recursion that leads to stack exhaustion.
Mitigation strategies for this vulnerability should prioritize immediate deployment of the patched version of Avahi software, specifically versions greater than 0.9rc2 where the fix has been implemented. System administrators should conduct comprehensive vulnerability assessments to identify all systems running affected versions of Avahi and ensure proper patch management procedures are in place to maintain up-to-date service discovery implementations. Network monitoring solutions should be configured to detect unusual mDNS traffic patterns that might indicate exploitation attempts, particularly looking for self-referential CNAME records in multicast DNS responses. The implementation of proper network segmentation and access controls can help limit the potential impact of such attacks by reducing the attack surface within local network segments. From an ATT&CK framework perspective, this vulnerability relates to T1499.004, which covers "Domain Name System (DNS) Tunneling," and represents a denial of service vector that can be leveraged to disrupt network services through resource exhaustion. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious mDNS traffic patterns, particularly those involving recursive DNS record structures that could indicate exploitation attempts. Regular security testing of network services and proper input validation procedures should be maintained to prevent similar recursion-based vulnerabilities from emerging in other network components that handle DNS-like protocols.