CVE-2026-2261
Published: 09 March 2026
Summary
CVE-2026-2261 is a high-severity Missing Release of Resource after Effective Lifetime (CWE-772) vulnerability in Freebsd Freebsd. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Service Exhaustion Flood (T1499.002); ranked at the 27.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SC-6 (Resource Availability).
Deeper analysis
CVE-2026-2261 affects blocklistd, a FreeBSD component that manages IP blocking based on adverse events. Due to a programming error, blocklistd leaks a socket descriptor for each adverse event report it receives. Once a threshold of leaked sockets is reached, blocklistd forks a child process to run its helper script, but the child dereferences a null pointer and crashes before executing it, preventing the blocking or unblocking of IP addresses. At a higher threshold, blocklistd becomes unable to receive new adverse event reports.
The vulnerability enables a denial-of-service attack, as an unauthenticated remote attacker can trigger a large number of adverse events from sacrificial IP addresses to exhaust resources and disable blocklistd before launching further attacks. This aligns with its CVSS v3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), reflecting network accessibility, low attack complexity, no privileges needed, and high availability impact via CWE-772 (Missing Release of Resource). Normal operations also generate adverse events that gradually degrade blocklistd's effectiveness, with leaked sockets potentially causing broader system slowdowns until restart.
The FreeBSD Security Advisory (https://security.freebsd.org/advisories/FreeBSD-SA-26:03.blocklistd.asc) provides details on patches and mitigation steps.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-10332
Vulnerability details
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Resource exhaustion via adverse event flooding directly enables service exhaustion DoS (T1499.002) and disables the blocklistd security tool (T1562.001).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Flaw remediation directly mitigates the programming error causing socket descriptor leaks and null pointer dereference in blocklistd by applying vendor patches.
Denial-of-service protection implements rate limiting and traffic filtering on adverse event reports to prevent resource exhaustion attacks targeting blocklistd.
Resource availability enforces limits on file descriptors and allocates dedicated resources to blocklistd, preventing unauthorized depletion from leaked sockets.