sshd-session (sshd on conect) crashes with signal 6

Hello!

After one week following current I recently started experiencing
sshd-session crashes on 2 machines running latest 15.0-PRERELEASE (git Main branch).

Anytime I try to SSH login to my 15.0-PRERELASE, sshd crashes on  sshd-sesson subprocess with:

pid 1217 (sshd-session), jid 0, uid 0: exited on signal 6

More details:

gdb /usr/libexec/sshd-session  /sshd-session.core

Core was generated by `sshd-session: ansible [priv]'.                                                                      
Program terminated with signal SIGABRT, Aborted.                                                                           
Sent by thr_kill() from pid 15843 and user 0.                                                                              
#0  thr_kill () at thr_kill.S:4                                                                                                                                                                                                                       
warning: Source file is more recent than executable.
4       RSYSCALL(thr_kill)                                   
(gdb) bt                                                                                                                   
#0  thr_kill () at thr_kill.S:4
#1  0x000019ceda634fa4 in __raise (s=s@entry=6) at /usr/src/lib/libc/gen/raise.c:48
#2  0x000019ceda6e52a9 in abort () at /usr/src/lib/libc/stdlib/abort.c:61
#3  0x000019ceda617d51 in __assert (func=<optimized out>, file=<optimized out>, line=line@entry=134, 
    failedexpr=<optimized out>) at /usr/src/lib/libc/gen/assert.c:47
#4  0x000019c6b21029c3 in temporarily_use_uid (pw=pw@entry=0x3c3261215280) at /usr/src/crypto/openssh/uidswap.c:134
#5  0x000019c6b20e8517 in user_key_allowed2 (pw=0x3c3261215280, key=0x3c32612e5820, 
    file=0x3c3261233e30 "/home/ansible/.ssh/authorized_keys", remote_ip=0x3c3261212da0 "192.168.122.1", 
    remote_host=0x3c3261212dd0 "192.168.122.1", authoptsp=0x19ced2ed0590) at /usr/src/crypto/openssh/auth2-pubkey.c:599
#6  user_key_allowed (ssh=ssh@entry=0x3c32612f4000, pw=0x3c3261215280, key=0x3c32612e5820, auth_attempt=<optimized out>, 
    authoptsp=authoptsp@entry=0x19ced2ed0688) at /usr/src/crypto/openssh/auth2-pubkey.c:783
#7  0x000019c6b20ed99d in mm_answer_keyallowed (ssh=0x3c32612f4000, sock=7, m=0x3c3261214d40)
    at /usr/src/crypto/openssh/monitor.c:1205
#8  0x000019c6b20f034d in monitor_read (ssh=ssh@entry=0x3c32612f4000, pmonitor=pmonitor@entry=0x3c32612c4cc0, 
    ent=0x19c6b210a720 <mon_dispatch_proto20+208>, pent=pent@entry=0x19ced2ed0758)
    at /usr/src/crypto/openssh/monitor.c:523
#9  0x000019c6b20efdf2 in monitor_child_preauth (ssh=ssh@entry=0x3c32612f4000, pmonitor=0x3c32612c4cc0)
    at /usr/src/crypto/openssh/monitor.c:298
#10 0x000019c6b20cac27 in privsep_preauth (ssh=ssh@entry=0x3c32612f4000) at /usr/src/crypto/openssh/sshd-session.c:353
#11 0x000019c6b20c9e3b in main (ac=2, av=<optimized out>) at /usr/src/crypto/openssh/sshd-session.c:1322
(gdb) q


Encountered on 2 machines:

Machine 1 "fbsd-next":

uname -v        -> FreeBSD 15.0-PRERELEASE #1 main-n279622-c992ac621327: Fri Aug 15 12:55:01 CEST 2025     root@fbsd-next:/usr/obj/usr/src/amd64.amd64/sys/GENERIC
freebsd-version ->  15.0-PRERELEASE
uname -UK       -> 1500060 1500060
git branch -v   -> * main c992ac621327 ipheth(4): Add CDC-NCM support for RX
git describe    -> vendor/NetBSD/bmake/20250804-302114-gc992ac621327


(Machine 2 is currently rebuilding):

git branch -v -> * main 5205b32de3fb libc: Drop incorrect qsort optimization
git describe  -> vendor/NetBSD/bmake/20250804-302115-g5205b32de3fb

Is anybody else experiencing same problem?

Best regards
  --Henryk Paluch