Reproducing the bug

$ apt-cache policy snmpd
snmpd:
  Installed: 5.8+dfsg-2ubuntu2.7
  Candidate: 5.8+dfsg-2ubuntu2.7
  Version table:
 *** 5.8+dfsg-2ubuntu2.7 500
        500 http://br.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        100 /var/lib/dpkg/status

The query timed out:
$ snmpget -v 1 -c public localhost 1.3.6.1.4.1.8072.9999.9999.3.0
Timeout: No Response from localhost.


The python agentx however got it, and later couldn't reconnect to snmpd:
2023-07-12 16:39:59,471 - pyagentx.network - INFO - Received GET PDU
2023-07-12 16:39:59,471 - pyagentx.network - INFO - SLEEP
2023-07-12 16:40:00,573 - pyagentx.network - INFO - Received GET PDU
2023-07-12 16:40:00,574 - pyagentx.network - INFO - SLEEP
2023-07-12 16:40:01,675 - pyagentx.network - INFO - Received GET PDU
2023-07-12 16:40:01,675 - pyagentx.network - INFO - SLEEP
2023-07-12 16:40:02,778 - pyagentx.network - ERROR - Network error, master disconnect?!

That's because snmpd crashed:
Jul 12 16:38:59 f-snmp-dbl-free systemd[1]: Started Simple Network Management Protocol (SNMP) Daemon..
Jul 12 16:40:00 f-snmp-dbl-free snmpd[3431]: Unknown operation 6 in agentx_got_response
Jul 12 16:40:01 f-snmp-dbl-free snmpd[3431]: Unknown operation 6 in agentx_got_response
Jul 12 16:40:01 f-snmp-dbl-free snmpd[3431]: malloc(): smallbin double linked list corrupted
Jul 12 16:40:01 f-snmp-dbl-free systemd[1]: snmpd.service: Main process exited, code=dumped, status=6/ABRT
Jul 12 16:40:01 f-snmp-dbl-free systemd[1]: snmpd.service: Failed with result 'core-dump'.

I ran it again, and got a different crash (this one wasn't listed in the SRU test plan):
Jul 12 16:42:15 f-snmp-dbl-free snmpd[4211]: Unknown operation 6 in agentx_got_response
Jul 12 16:42:16 f-snmp-dbl-free snmpd[4211]: corrupted size vs. prev_size
Jul 12 16:42:16 f-snmp-dbl-free systemd[1]: snmpd.service: Main process exited, code=dumped, status=6/ABRT
Jul 12 16:42:16 f-snmp-dbl-free systemd[1]: snmpd.service: Failed with result 'core-dump'.

And a third time got me this third type of error message and a crash:
Jul 12 16:43:11 f-snmp-dbl-free systemd[1]: Starting Simple Network Management Protocol (SNMP) Daemon....
Jul 12 16:43:11 f-snmp-dbl-free systemd[1]: Started Simple Network Management Protocol (SNMP) Daemon..
Jul 12 16:43:16 f-snmp-dbl-free snmpd[4379]: Unknown operation 6 in agentx_got_response
Jul 12 16:43:23 f-snmp-dbl-free snmpd[4379]: malloc(): unsorted double linked list corrupted
Jul 12 16:43:23 f-snmp-dbl-free systemd[1]: snmpd.service: Main process exited, code=dumped, status=6/ABRT
Jul 12 16:43:23 f-snmp-dbl-free systemd[1]: snmpd.service: Failed with result 'core-dump'.


And a fourth error message plus crash:
Jul 12 16:44:47 f-snmp-dbl-free snmpd[4488]: free(): double free detected in tcache 2
Jul 12 16:44:47 f-snmp-dbl-free systemd[1]: snmpd.service: Main process exited, code=dumped, status=6/ABRT
Jul 12 16:44:47 f-snmp-dbl-free systemd[1]: snmpd.service: Failed with result 'core-dump'.

I tried a few more times, but these are the four types of crashes I could get.

With the packages from proposed:
$ apt-cache policy snmpd
snmpd:
  Installed: 5.8+dfsg-2ubuntu2.8
  Candidate: 5.8+dfsg-2ubuntu2.8
  Version table:
 *** 5.8+dfsg-2ubuntu2.8 500
        500 http://br.archive.ubuntu.com/ubuntu focal-proposed/main amd64 Packages
        100 /var/lib/dpkg/status

I ran the snmpget command dozen of times, and unfortunately I did find a new crash:
Jul 12 16:46:58 f-snmp-dbl-free systemd[1]: Started Simple Network Management Protocol (SNMP) Daemon..
Jul 12 16:48:46 f-snmp-dbl-free snmpd[4937]: double free or corruption (fasttop)
Jul 12 16:48:47 f-snmp-dbl-free systemd[1]: snmpd.service: Main process exited, code=dumped, status=6/ABRT
Jul 12 16:48:47 f-snmp-dbl-free systemd[1]: snmpd.service: Failed with result 'core-dump'.

At this point I can't say for sure it was introduced by the patches, but this is verification failed according to the test plan.