# CVE-2025-39773

## Summary

- **CVE ID:** CVE-2025-39773
- **Severity:** MEDIUM
- **CVSS Score:** 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2025
- **Last Modified:** Sep 8, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

net: bridge: fix soft lockup in br_multicast_query_expired()

When set multicast_query_interval to a large value, the local variable
'time' in br_multicast_send_query() may overflow. If the time is smaller
than jiffies, the timer will expire immediately, and then call mod_timer()
again, which creates a loop and may trigger the following soft lockup
issue.

  watchdog: BUG: soft lockup - CPU#1 stuck for 221s! [rb_consumer:66]
  CPU: 1 UID: 0 PID: 66 Comm: rb_consumer Not tainted 6.16.0+ #259 PREEMPT(none)
  Call Trace:
   <IRQ>
   __netdev_alloc_skb+0x2e/0x3a0
   br_ip6_multicast_alloc_query+0x212/0x1b70
   __br_multicast_send_query+0x376/0xac0
   br_multicast_send_query+0x299/0x510
   br_multicast_query_expired.constprop.0+0x16d/0x1b0
   call_timer_fn+0x3b/0x2a0
   __run_timers+0x619/0x950
   run_timer_softirq+0x11c/0x220
   handle_softirqs+0x18e/0x560
   __irq_exit_rcu+0x158/0x1a0
   sysvec_apic_timer_interrupt+0x76/0x90
   </IRQ>

This issue can be reproduced with:
  ip link add br0 type bridge
  echo 1 > /sys/class/net/br0/bridge/multicast_querier
  echo 0xffffffffffffffff >
  	/sys/class/net/br0/bridge/multicast_query_interval
  ip link set dev br0 up

The multicast_startup_query_interval can also cause this issue. Similar to
the commit 99b40610956a ("net: bridge: mcast: add and enforce query
interval minimum"), add check for the query interval maximum to fix this
issue.

## Affected Products

- Linux — Linux (d902eee43f1951b358d7347d9165c6af21cf7b1b)
- Linux — Linux (2.6.34)
- Linux — Linux (0)
- Linux — Linux (5.15.190)
- Linux — Linux (6.1.149)
- Linux — Linux (6.6.103)
- Linux — Linux (6.12.44)
- Linux — Linux (6.16.4)
- Linux — Linux (6.17)

## References

- [CNA](https://git.kernel.org/stable/c/34171b9e53bd1dc264f5556579f2b04f04435c73)
- [CNA](https://git.kernel.org/stable/c/43e281fde5e76a866a4d10780c35023f16c0e432)
- [CNA](https://git.kernel.org/stable/c/96476b043efb86a94f2badd260f7f99c97bd5893)
- [CNA](https://git.kernel.org/stable/c/bdb19cd0de739870bb3494c815138b9dc30875c4)
- [CNA](https://git.kernel.org/stable/c/5bf5fce8a0c2a70d063af778fdb5b27238174cdd)
- [CNA](https://git.kernel.org/stable/c/d1547bf460baec718b3398365f8de33d25c5f36f)
- [CVE](https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-082556.html)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-032379.html)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.12%
- **EPSS Percentile:** 2.1

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._