Technical Tip: FortiAP may go offline due to cwWtpd crash when IGMP snooping is enabled on SSIDs under high client density

Description

This article describes an issue where FortiAP models FortiAP-431G, FortiAP-433G, and FortiAP-233G running firmware v7.6.5 or v8.0.0 may unexpectedly go offline when handling a high number of connected clients.

The issue has been observed when the FortiAP is servicing approximately 60 to 80 clients per radio, and IGMP snooping is enabled on one or more SSIDs broadcast by the affected AP.

Scope

Affected FortiAP models: FortiAP-431G, FortiAP-433G, FortiAP-233G.

Affected firmware: v7.6.5, v8.0.0.

Conditions: 

• IGMP snooping is enabled on one or more SSIDs broadcast by the affected FortiAPs.

• High wireless client concurrency, usually around 60 to 80 clients per radio.

Fixed versions:

• FortiAP v7.6.6 build1115 or later.

• FortiAP v8.0.1 build0051 or later.

Solution

When the issue occurs, the cwWtpd process crashes with a segmentation fault. As a result, the CAPWAP tunnel between the FortiAP and the FortiGate wireless controller goes down, causing the AP to appear offline and disconnecting all associated wireless clients.

Example crash signature from the FortiAP technical logs:

285: 2026-06-25 10:01:31 <13397> *** signal 11 (Segmentation fault) received ***
286: 2026-06-25 10:01:31 <13397> Register dump:
287: 2026-06-25 10:01:31 <13397> $ 0: 9742ac93cc060000 7fba28ac30 7fba28ac30 00000001
288: 2026-06-25 10:01:31 <13397> $ 4: 00000000 00000004 0d07b538 00000000
289: 2026-06-25 10:01:31 <13397> $ 8: 00000000 000f4240 7ffffffffffffffe ffffffff
290: 2026-06-25 10:01:31 <13397> $12: 1699f8f99f ffffffffffffffff ffffffffffffffff 00000860
291: 2026-06-25 10:01:31 <13397> $16: 7fba204ff8 7fb9cc2d90 00000000 00000076
292: 2026-06-25 10:01:31 <13397> $20: 00000001 7fca186d58 004008ac 000000f8
293: 2026-06-25 10:01:31 <13397> $24: 7fba475000 7fba475cb0 7fca186d58 7fba475000
294: 2026-06-25 10:01:31 <13397> $28: 7fba475000 7fca185c70 7fb9cc1d5c
295: 2026-06-25 10:01:31 <13397> sp: 7fca185c60 pc: 7fb9cc1d08
296: 2026-06-25 10:01:31 <13397> pstate: a0000000 fault_addr: 42ac93cc060008
297: 2026-06-25 10:01:31 <13397> Backtrace:

As a workaround, disable IGMP snooping on all SSIDs broadcast by the affected FortiAPs.

After disabling IGMP snooping, monitor the FortiAP to confirm that the CAPWAP tunnel remains stable and that no new cwWtpd segmentation fault crash logs are generated.

As a permanent solution, upgrade the affected FortiAPs to one of the fixed firmware versions:

• FortiAP v7.6.6 build1115 or later.

• FortiAP v8.0.1 build0051 or later.