$ dd if=/dev/random of=prefix bs=1024 count=10
10+0 records in
10+0 records out
10240 bytes (10 kB, 10 KiB) copied, 0.000207353 s, 49.4 MB/s
$ dd if=/dev/random of=suffix bs=1024 count=10
10+0 records in
10+0 records out
10240 bytes (10 kB, 10 KiB) copied, 0.000172483 s, 59.4 MB/s
$ touch foo
$ 7za -t7z a foo.7z foo

7-Zip (a) [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,64 bits,4 CPUs AMD EPYC-Rome Processor (830F10),ASM,AES-NI)

Scanning the drive:
1 file, 0 bytes

Creating archive: foo.7z

Items to compress: 1


Files read from disk: 0
Archive size: 82 bytes (1 KiB)
Everything is Ok
$ cat prefix foo.7z suffix > middle.bin
$ 7za l middle.bin

7-Zip (a) [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,64 bits,4 CPUs AMD EPYC-Rome Processor (830F10),ASM,AES-NI)

Scanning the drive for archives:
1 file, 20562 bytes (21 KiB)

Listing archive: middle.bin

--
Path = middle.bin
Type = 7z
WARNINGS:
There are data after the end of archive
Offset = 10240
Physical Size = 82
Tail Size = 10240
Headers Size = 82
Solid = -
Blocks = 0

   Date      Time    Attr         Size   Compressed  Name
------------------- ----- ------------ ------------  ------------------------
2024-12-25 21:26:30 ....A            0            0  foo
------------------- ----- ------------ ------------  ------------------------
2024-12-25 21:26:30                  0            0  1 files

Warnings: 1
$