CVE-2026-71401 in wicked
Summary
by MITRE • 08/27/2026
An integer underflow was found in the DHCPv4 packet capture code of wicked. ni_capture_inspect_udp_header() in src/capture.c does not verify that the IP total length field (ip_len) is at least as large as the IP header length (ihl) before subtracting the header length. An unauthenticated attacker on the same network can thereby trigger an out-of-bounds read past the receive buffer in the wicked DHCPv4 client (wickedd-dhcp4), which can crash the daemon depending on the process memory layout. No information disclosure has been demonstrated. This issue affects wicked up to and including version 0.6.80.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified as an integer underflow within the wicked DHCPv4 packet capture subsystem represents a critical flaw in input validation logic, specifically located in the ni_capture_inspect_udp_header function found in src/capture.c. This component is responsible for parsing incoming network packets to extract relevant data for the Dynamic Host Configuration Protocol version 4 client daemon, known as wickedd-dhcp4. The core technical deficiency lies in the failure of the code to verify that the Internet Protocol total length field, denoted as ip_len, is greater than or equal to the IP header length, referred to as ihl, prior to performing a subtraction operation. In standard IPv4 packet structures, the total length indicates the entire size of the packet including headers and data, while the header length specifies only the size of the IP header itself. The difference between these two values should theoretically yield the payload size. However, because the code does not enforce that ip_len is at least as large as ihl, a crafted or malformed packet with an unusually small total length field can cause the subtraction result to wrap around due to integer underflow characteristics inherent in unsigned arithmetic operations commonly used in low-level network processing libraries.
This mathematical error leads directly to an out-of-bounds read condition within the memory space allocated for receiving packets. When the calculated payload size is erroneously large or negative depending on interpretation, subsequent buffer access routines may attempt to read data beyond the boundaries of the receive buffer. This behavior constitutes a classic CWE-190 integer overflow/underflow vulnerability that cascades into CWE-125 out-of-bounds read. The operational impact of this flaw allows an unauthenticated attacker positioned on the same local network segment to trigger arbitrary memory reads by sending specially crafted DHCPv4 packets. While current analysis indicates that no information disclosure has been demonstrated, meaning sensitive data from adjacent memory regions is not necessarily exfiltrated, the primary consequence remains a denial of service condition. Depending on the specific process memory layout and heap state at the time of exploitation, this out-of-bounds access can cause the wickedd-dhcp4 daemon to crash or become unstable, effectively disrupting network configuration services for the host system.
From a threat modeling perspective aligned with MITRE ATT&CK frameworks, this vulnerability facilitates local denial of service attacks through packet injection techniques often categorized under resource exhaustion or component failure vectors. The attack vector is classified as adjacent because it requires the attacker to be on the same broadcast domain or network segment where DHCP traffic is visible and interceptable without requiring routing traversal across untrusted networks. This proximity requirement limits the scope but does not diminish the severity for devices connected via Ethernet or Wi-Fi, which are common targets for rogue access point attacks or man-in-the-middle scenarios in public or corporate environments. The lack of authentication requirements further exacerbates the risk, as any device on the local network can attempt to exploit this flaw without prior credentials.
Mitigation strategies must focus primarily on updating the wicked software package to a version that includes patches addressing these validation checks. Users running versions up to and including 0.6.80 are advised to apply vendor-provided updates immediately upon availability, as newer releases typically implement strict bounds checking before arithmetic operations involving packet header fields. In environments where immediate patching is not feasible, network segmentation can serve as a temporary compensating control by restricting DHCP traffic to trusted subnets or employing firewall rules that drop malformed packets with suspiciously low total length values relative to their headers. Additionally, deploying intrusion detection systems configured to identify anomalous UDP payload sizes in DHCP broadcasts may help mitigate the risk of exploitation until permanent fixes are deployed across all affected endpoints.