CVE-2025-39773: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-39773 is a vulnerability discovered in the Linux kernel's network bridge multicast functionality, disclosed on September 11, 2025. The issue affects the brmulticastquery_expired() function when handling large multicast query intervals (NVD).

The vulnerability occurs when the multicastqueryinterval is set to a large value, causing the local variable 'time' in brmulticastsendquery() to overflow. If the time value becomes smaller than jiffies, the timer expires immediately and triggers modtimer() again, creating a loop that results in a soft lockup condition. This can lead to CPU being stuck for extended periods, as evidenced by the reported 221-second lockup in testing (NVD).

The vulnerability can cause system performance degradation through CPU soft lockups, potentially affecting system stability and availability. The issue specifically impacts systems using Linux kernel bridge networking with multicast functionality enabled (Ubuntu).

The issue has been addressed by adding a check for the query interval maximum, similar to the previous commit that added and enforced query interval minimum. The fix prevents the timer overflow condition by implementing proper bounds checking (NVD).