CVE-2026-18313 in libpcap
Summary
by MITRE • 09/05/2026
rpcapd can allocate up to 65536 bytes per each RPCAP_MSG_UPDATEFILTER_REQ or RPCAP_MSG_STARTCAP_REQ message received from the client, but it never frees the memory, so it leaks memory even under normal use. A malicious client can cause the server to leak memory substantially faster.
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Analysis
by VulDB Data Team • 09/05/2026
The rpcapd daemon, a core component of the Remote Packet Capture Protocol used primarily with tools like Wireshark and tcpdump for network analysis, contains a critical resource management flaw that leads to progressive memory exhaustion. This vulnerability stems from an improper handling of dynamic memory allocation within the server-side processing logic for specific control messages. Specifically, when the daemon receives RPCAP_MSG_UPDATEFILTER_REQ or RPCAP_MSG_STARTCAP_REQ messages from a connected client, it allocates up to 65536 bytes of heap memory to handle the request parameters and state management associated with that session. Under normal operational conditions, this memory should be released upon completion of the task or termination of the connection. However, due to a logic error in the cleanup routines, the allocated buffer is never deallocated, resulting in a persistent memory leak for every such message processed by the server.
This flaw represents a classic instance of CWE-401, which describes missing release of memory after effective lifetime, often referred to as a memory leak. The severity of this issue is amplified because it can be triggered remotely without authentication if the rpcapd service is configured to allow unauthenticated connections or if an attacker gains access to the network segment where the daemon resides. A malicious actor does not need complex exploitation techniques; they simply need to send a high volume of these specific RPCAP messages to the vulnerable server. Each message consumes additional memory that remains resident in the system's RAM, gradually depleting available resources. This behavior aligns with ATT&CK technique T1498, Network Denial of Service, as it allows an attacker to degrade or completely halt service availability by exhausting system memory reserves.
The operational impact of this vulnerability is significant for any organization relying on remote packet capture capabilities for network monitoring, intrusion detection, or forensic analysis. As the daemon continues to leak memory, the host operating system may begin swapping heavily to disk, leading to severe performance degradation and latency in other critical services running on the same machine. Eventually, the process will consume all available physical RAM and swap space, causing the rpcapd service to crash due to an out-of-memory condition or forcing the entire operating system to become unresponsive. This denial of service effect disrupts network visibility and can mask malicious activity that relies on timing or stealth, as administrators may be too busy troubleshooting infrastructure issues to notice ongoing attacks.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The most effective solution is to apply vendor-provided patches that correct the memory deallocation logic within the rpcapd source code. Organizations should ensure they are running the latest stable version of their packet capture software suite, as this vulnerability has been addressed in subsequent releases where proper cleanup routines were implemented for all message types. In environments where patching is not immediately feasible, network segmentation and firewall rules should be employed to restrict access to rpcapd ports (typically UDP port 2001) to only trusted management stations or specific IP addresses. Additionally, configuring the daemon to require authentication can prevent unauthenticated attackers from triggering the memory leak, although this does not mitigate risks posed by compromised authorized clients. Regular monitoring of system resource usage and process stability is recommended to detect early signs of such resource exhaustion attacks.