Escaping Containment: a Security Analysis of Freebsd Jails [video]
Key topics
A recent security analysis of FreeBSD jails has uncovered around 50 distinct issues across multiple kernel subsystems, sparking a lively debate about the challenges of maintaining strict isolation. While some commenters expressed concern over the sheer number of issues, others pointed out that most don't necessarily become exploitable vulnerabilities, and that the researchers assumed a "compromised jail" as a starting point. The discussion highlights the complexities of ensuring security in complex systems, with one commenter noting that the lack of real liability for getting hacked and inadequate software development budgets exacerbate the problem. As the community digests the findings, the thread is buzzing with interest, with many praising the researchers' systematic approach to identifying potential vulnerabilities.
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Dec 30, 2025 at 2:15 PM EST
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> ... we conducted a large-scale audit of FreeBSD kernel code paths accessible from within a jail. We systematically examined privileged operations, capabilities, and interfaces that a jailed process can still reach, hunting for memory safety issues, race conditions, and logic flaws. The result: roughly 50 distinct issues uncovered across multiple kernel subsystems, ranging from buffer overflows and information leaks to unbounded allocations and reference counting errors—many of which could crash the system or provide vectors for privilege escalation beyond the jail.
> We’ve developed proof-of-concept exploits and tools to demonstrate some of these vulnerabilities in action. We’ve responsibly disclosed our findings to the FreeBSD security team and are collaborating with them on fixes. Our goal isn’t to break FreeBSD, but to highlight the systemic difficulty of maintaining strict isolation in a large, mature codebase.
> Our goal isn’t to break FreeBSD, but to highlight the systemic difficulty of maintaining strict isolation in a large, mature codebase.
50 distinct issues? That's devastating. If these researchers found 50 issues, we all know there's more that 50 issues in the codebase.
I really think we need to start seriously considering using SeL4 as a base for our operating systems. Or something like it. We can't keep building on top of sand.
That's rough but for a systematic search of a large system it seems reasonable. Theres a good chance that these 50 represent most the "easy" vulnerabilities if the researchers did a thorough job. In a way it seems more likely than if they found a smaller number.
His process is briefly touched on in the talk. If I understood correctly he compiled a list of the most common jail privilege flags that exist and then searched the FreeBSD source code for those, investigating the code in those places. No automated tooling was used, this was just done by reading the source code. Which Ilja has been doing as “light bed time reading” :p for as long as I’ve known him (25+ years).
Someone just did a great work on security audit and made FreeBSD Jails a lot more secure.
This is what security audits are for.