EUVD-2026-39964Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local low-priv account (AV:L/PR:L); AC:H because exploitation requires winning a kernel lock race; full kernel compromise yields C/I/A:H.
Primary rating from Vendor (freebsd).
CVSS VectorVendor: freebsd
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
3DescriptionCVE.org
The kernel handler for IPV6_MSFILTER dropped a serializing lock in order to copy the source-filter list from userspace, then reacquired the lock. During this window another thread could free the multicast filter structure, leaving the handler with a stale pointer to freed memory.
An unprivileged local user can exploit this use-after-free to escalate privileges.
AnalysisAI
Local privilege escalation in the FreeBSD kernel arises from a use-after-free in the IPv6 multicast source-filter handler (IPV6_MSFILTER), affecting FreeBSD 14.3, 14.4, and 15.0 releases before their respective patch levels. An unprivileged local user can win a race against the handler's dropped-then-reacquired serializing lock to free the multicast filter structure out from under the kernel, corrupting memory to gain root-level control. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a local unprivileged account on the FreeBSD host able to make IPv6 socket calls and invoke the IPV6_MSFILTER setsockopt option; the attacker must win the race in which the kernel handler drops and reacquires its serializing lock around the userspace copyin of the source-filter list, and concurrently free the multicast filter structure in that window. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | Signals are coherent and point to a serious-but-not-urgent issue. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A user with an unprivileged local shell account (or code running inside a jail/container) opens an IPv6 socket and repeatedly issues IPV6_MSFILTER setsockopt calls while a second thread concurrently frees the multicast filter structure during the handler's unlocked copyin window. By winning this race and grooming the freed kernel memory, the attacker forces the kernel to operate on a controlled stale pointer, corrupting kernel state to escalate to root. … |
| Remediation | Apply the vendor-released patch by updating to the fixed patch level for your branch: FreeBSD 14.3-RELEASE-p15, 14.4-RELEASE-p6, or 15.0-RELEASE-p10 or later, using freebsd-update (binary update) or by recompiling the kernel from the patched source per FreeBSD-SA-26:29 (https://security.freebsd.org/advisories/FreeBSD-SA-26:29.ip6_multicast.asc); a reboot is required for the new kernel to take effect. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all systems running FreeBSD 14.3, 14.4, or 15.0; audit local user accounts and disable those not operationally required; document current administrative access. …
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Same weakness CWE-416 – Use After Free
View allSame technique Memory Corruption
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External POC / Exploit Code
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