Description

This vulnerability is of type use-after-free. And after quick investigation I think it is very likely to be successfully exploited to remote code execution.
The bug exists in latest stable release (radare2-5.5.4) and lastest master branch (ed2030b79e68986bf04f3a6279463ab989fe400f, updated in Jan 22, 2022). Specifically, the vulnerable code (located at libr/bin/format/pyc/marshal.c) and the bug’s basic explanation are highlighted as follows:

// libr/bin/format/pyc/marshal.c
static pyc_object *get_object(RBuffer *buffer) {
...
// line 1114
// the ref_idx->data points to an already freed memory block!
		if (ref_idx->data != ret) {
            // this bug might be exploited since program will call dangerous functions like free in the following function
            // in a released version of radare2 (no address sanitizer)
			free_object (ref_idx->data);

Proof of Concept

Build the radare2 (5.5.4 or latest commit ed2030b79e68986bf04f3a6279463ab989fe400f) and run it using the input POC.

# build the radare2 with address sanitizer
export CFLAGS=" -fsanitize=address "; export CXXFLAGS=" -fsanitize=address "; export LDFLAGS=" -fsanitize=address ";
CFGARG=" --enable-shared=no " PREFIX=`realpath install` bash sys/build.sh
# disable some features of address sanitizer to avoid false positives
export ASAN_OPTIONS=detect_leaks=0:abort_on_error=1:symbolize=0:allocator_may_return_null=1:detect_odr_violation=0
# trigger the crash
./radare2 -A -q POC_FILE

The crash stack is:

=================================================================
==18153==ERROR: AddressSanitizer: heap-use-after-free on address 0x60300008b3f0 at pc 0x7ffff2c29c25 bp 0x7fffffffd0f0 sp 0x7fffffffd0e8
READ of size 8 at 0x60300008b3f0 thread T0
    #0 0x7ffff2c29c24  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x86bc24)
    #1 0x7ffff2c1dc21  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x85fc21)
    #2 0x7ffff2c23427  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x865427)
    #3 0x7ffff2c204db  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x8624db)
    #4 0x7ffff2c1b7b3  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x85d7b3)
    #5 0x7ffff2599d94  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x1dbd94)
    #6 0x7ffff2598054  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x1da054)
    #7 0x7ffff257df9e  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x1bff9e)
    #8 0x7ffff252179b  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x16379b)
    #9 0x7ffff2520876  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x162876)
    #10 0x7ffff386facc  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_core.so+0x692acc)
    #11 0x7ffff76312ae  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_main.so+0x992ae)
    #12 0x7ffff73a50b2  (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #13 0x55555557239d  (/src/projects/radare2-5.5.4/lastest-radare2/install/bin/radare2+0x1e39d)

0x60300008b3f0 is located 0 bytes inside of 24-byte region [0x60300008b3f0,0x60300008b408)
freed by thread T0 here:
    #0 0x5555555ed392  (/src/projects/radare2-5.5.4/lastest-radare2/install/bin/radare2+0x99392)
    #1 0x7ffff78af77d  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_util.so+0x23277d)
    #2 0x7ffff2c1d50a  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x85f50a)
    #3 0x7ffff2c227b5  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x8647b5)
    #4 0x7ffff2c1dc21  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x85fc21)
    #5 0x7ffff2c23427  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x865427)
    #6 0x7ffff2c204db  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x8624db)

previously allocated by thread T0 here:
    #0 0x5555555ed772  (/src/projects/radare2-5.5.4/lastest-radare2/install/bin/radare2+0x99772)
    #1 0x7ffff78a8889  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_util.so+0x22b889)
    #2 0x7ffff2c1dc21  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x85fc21)
    #3 0x7ffff2c23427  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x865427)
    #4 0x7ffff2c204db  (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x8624db)

SUMMARY: AddressSanitizer: heap-use-after-free (/src/projects/radare2-5.5.4/lastest-radare2/install/lib/libr_bin.so+0x86bc24)
Shadow bytes around the buggy address:
  0x0c0680009620: 00 00 fa fa 00 00 00 fa fa fa 00 00 00 00 fa fa
  0x0c0680009630: 00 00 00 00 fa fa 00 00 00 00 fa fa 00 00 00 fa
  0x0c0680009640: fa fa 00 00 00 fa fa fa 00 00 00 00 fa fa 00 00
  0x0c0680009650: 00 00 fa fa 00 00 00 00 fa fa fd fd fd fa fa fa
  0x0c0680009660: fd fd fd fa fa fa fd fd fd fa fa fa fd fd fd fa
=>0x0c0680009670: fa fa fd fd fd fa fa fa fd fd fd fa fa fa[fd]fd
  0x0c0680009680: fd fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c0680009690: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c06800096a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c06800096b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c06800096c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==18153==ABORTING

Program received signal SIGABRT, Aborted.
0x00007ffff73c418b in raise () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0  0x00007ffff73c418b in raise () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007ffff73a3859 in abort () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x000055555560ba77 in __sanitizer::Abort() ()
#3  0x0000555555609fa1 in __sanitizer::Die() ()
#4  0x00005555555f14e4 in __asan::ScopedInErrorReport::~ScopedInErrorReport() ()
#5  0x00005555555f30aa in __asan::ReportGenericError(unsigned long, unsigned long, unsigned long, unsigned long, bool, unsigned long, unsigned int, bool) ()
#6  0x00005555555f3948 in __asan_report_load8 ()
#7  0x00007ffff2c29c25 in get_object (buffer=<optimized out>) at /src/projects/radare2-5.5.4/lastest-radare2/libr/../libr/bin/p/../format/pyc/marshal.c:1114
#8  0x00007ffff2c1dc22 in get_code_object (buffer=<optimized out>) at /src/projects/radare2-5.5.4/lastest-radare2/libr/../libr/bin/p/../format/pyc/marshal.c:953
#9  0x00007ffff2c23428 in get_object (buffer=<optimized out>) at /src/projects/radare2-5.5.4/lastest-radare2/libr/../libr/bin/p/../format/pyc/marshal.c:1032
#10 0x00007ffff2c204dc in get_sections_symbols_from_code_objects (buffer=<optimized out>, sections=<optimized out>, symbols=<optimized out>, cobjs=<optimized out>,
    magic=<optimized out>) at /src/projects/radare2-5.5.4/lastest-radare2/libr/../libr/bin/p/../format/pyc/marshal.c:1205
#11 0x00007ffff2c2e582 in pyc_get_sections_symbols (sections=0x7fffffffc130, symbols=0x0, cobjs=0x7ffff73c418b <raise+203>, buf=0x7fffffffc130, magic=0)
    at /src/projects/radare2-5.5.4/lastest-radare2/libr/../libr/bin/p/../format/pyc/pyc.c:7
#12 0x00007ffff2c1b7b4 in symbols (arch=<optimized out>) at /src/projects/radare2-5.5.4/lastest-radare2/libr/../libr/bin/p/bin_pyc.c:124
#13 0x00007ffff2599d95 in r_bin_object_set_items (bf=<optimized out>, o=<optimized out>) at bobj.c:326
#14 0x00007ffff2598055 in r_bin_object_new (bf=<optimized out>, plugin=<optimized out>, baseaddr=<optimized out>, loadaddr=<optimized out>, offset=<optimized out>,
    sz=<optimized out>) at bobj.c:168
#15 0x00007ffff257df9f in r_bin_file_new_from_buffer (bin=0x616000000980, file=<optimized out>, buf=<optimized out>, rawstr=<optimized out>, baseaddr=<optimized out>,
    loadaddr=<optimized out>, fd=<optimized out>, pluginname=<optimized out>) at bfile.c:560
#16 0x00007ffff252179c in r_bin_open_buf (bin=<optimized out>, buf=<optimized out>, opt=<optimized out>) at bin.c:279
#17 0x00007ffff2520877 in r_bin_open_io (bin=0x616000000980, opt=<optimized out>) at bin.c:339
#18 0x00007ffff386facd in r_core_file_do_load_for_io_plugin (r=0x7fffec332800, baseaddr=18446744073709551615, loadaddr=0) at cfile.c:435
#19 r_core_bin_load (r=0x7fffec332800, filenameuri=<optimized out>, baddr=<optimized out>) at cfile.c:636
#20 0x00007ffff76312af in r_main_radare2 (argc=<optimized out>, argv=<optimized out>) at radare2.c:1177
#21 0x00007ffff73a50b3 in __libc_start_main () from /lib/x86_64-linux-gnu/libc.so.6
#22 0x000055555557239e in _start ()

Impact

If address sanitizer is disabled during the compiling, the program should executes into the free_object function with an already freed memory block. Therefore I think it is very likely to be exploited by carefully manipulating the wild pointer ref_idx->data.
For more general description of use-after-free, see CWE.