FreeBSD Jail Ref Count Underflow Privilege Escalation
CVE-2026-49419 Published on August 19, 2026
Jail reference count underflow
When the JAIL_AT_DESC flag is specified, kern_jail_set() and kern_jail_get() released the reference to the caller's current prison before looking up the jail descriptor. If the descriptor lookup failed, error-handling paths released the same reference a second time.
An unprivileged local user can trigger a prison reference count underflow, which may cause the prison structure to be freed while still in use. When this is done on the jail host, the bug will generally result in an immediate panic. However, if the user is running in a jail, then it may be possible to exploit the bug to elevate privileges.
Vulnerability Analysis
CVE-2026-49419 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
Improper Update of Reference Count
The software uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count. Reference counts can be used when tracking how many objects contain a reference to a particular resource, such as in memory management or garbage collection. When the reference count reaches zero, the resource can be de-allocated or reused because there are no more objects that use it. If the reference count accidentally reaches zero, then the resource might be released too soon, even though it is still in use. If all objects no longer use the resource, but the reference count is not zero, then the resource might not ever be released.
Products Associated with CVE-2026-49419
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Affected Versions
FreeBSD:- Version 15.1-RELEASE and below p1 is affected.
- Version 15.0-RELEASE and below p11 is affected.