FreeBSD blocklistd resource consumption

Summaryinfo

A vulnerability was found in FreeBSD. It has been rated as problematic. Affected is an unknown function of the component blocklistd. The manipulation leads to resource consumption. This vulnerability is listed as CVE-2026-2261. The attack may be initiated remotely. There is no available exploit. To fix this issue, it is recommended to deploy a patch.

Detailsinfo

A vulnerability was found in FreeBSD (version unknown) and classified as problematic. This issue affects an unknown function of the component blocklistd. The manipulation with an unknown input leads to a resource consumption vulnerability. Using CWE to declare the problem leads to CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. Impacted is availability. The summary by CVE is:

Due to a programming error, blocklistd leaks a socket descriptor for each adverse event report it receives. Once a certain number of leaked sockets is reached, blocklistd becomes unable to run the helper script: a child process is forked, but this child dereferences a null pointer and crashes before it is able to exec the helper. At this point, blocklistd still records adverse events but is unable to block new addresses or unblock addresses whose database entries have expired. Once a second, much higher number of leaked sockets is reached, blocklistd becomes unable to receive new adverse event reports. An attacker may take advantage of this by triggering a large number of adverse events from sacrificial IP addresses to effectively disable blocklistd before launching an attack. Even in the absence of attacks or probes by would-be attackers, adverse events will occur regularly in the course of normal operations, and blocklistd will gradually run out file descriptors and become ineffective. The accumulation of open sockets may have knock-on effects on other parts of the system, resulting in a general slowdown until blocklistd is restarted.

It is possible to read the advisory at freebsd.org. The identification of this vulnerability is CVE-2026-2261. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 03/17/2026). The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Applying a patch is able to eliminate this problem. The bugfix is ready for download at security.FreeBSD.org.

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Productinfo

Type

• Operating System

Name

• FreeBSD

License

• open-source

Website

• Product: https://www.freebsd.org/

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