CVE-2026-2261 blocklistd(8) socket leak
An attacker can exhaust file descriptors in FreeBSD's blocklistd by triggering adverse events, disabling IP blocking and causing system slowdowns.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-2261?
CVE-2026-2261 is a high-severity denial of service vulnerability in Freebsd Freebsd, published on 9 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-772
Which versions are affected by CVE-2026-2261?
It affects 1 product.
Products include Freebsd Freebsd.
How do I fix CVE-2026-2261?
No fix has been published for CVE-2026-2261 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-2261 being exploited?
There is no known exploitation of CVE-2026-2261 in the wild and no public exploit code.
Other vulnerabilities in Freebsd Freebsd
Sources
Also known as GHSA-5cm6-5xpq-xrwv.