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When obfsproxy is configured with the following in torrc:

servertransportplugin obfs2 exec /usr/local/bin/obfsproxy --managed --log-file=/var/log/tor/obfsproxy.log --log-min-severity=debug

It immediately segfaults on startup, with the following stack trace:

Core was generated by `/usr/local/bin/obfsproxy --managed --log-file=/var/log/tor/obfsproxy.log --log-'.
Program terminated with signal 11, Segmentation fault.
#0  0x0000003ec1879b80 in strlen () from /lib64/libc.so.6
(gdb) bt
#0  0x0000003ec1879b80 in strlen () from /lib64/libc.so.6
#1  0x0000003ec1846cb9 in vfprintf () from /lib64/libc.so.6
#2  0x0000003ec18699da in vsnprintf () from /lib64/libc.so.6
#3  0x00000000004058b3 in obfs_vsnprintf (
    str=0x7fff872eb5e8 "0123456789abcdefghijklmnopqrstuvwxyz 0.0.0.0:42401 \301>", size=1, format=0x7fff872ebb08 " \337\314\020\377\377\377\377\002", args=0x0)
    at src/util.c:304
#4  0x0000000000405a0a in logv (severity=<value optimized out>, 
    format=0x40af0a "%s %s %s:%hu\n", ap=0x7fff872eba10) at src/util.c:530
#5  0x000000000040243e in print_protocol_line (
    format=0x40af0a "%s %s %s:%hu\n") at src/managed.c:152
#6  0x0000000000402570 in print_method_line (proxy=0x10cbf010)
    at src/managed.c:331
#7  open_listeners_managed (proxy=0x10cbf010) at src/managed.c:540
#8  0x0000000000402b5f in launch_server_listeners () at src/managed.c:594
#9  launch_listeners () at src/managed.c:650
#10 launch_managed_proxy () at src/managed.c:681
#11 0x0000000000402087 in obfs_main (argc=281861920, argv=0x1)
    at src/main.c:265
#12 0x0000003ec181d994 in __libc_start_main () from /lib64/libc.so.6
#13 0x0000000000401de9 in _start ()

100% reproducible in my environment. Core file available if needed.