OT: A self-extracting executable tiny ELF32 payload

["Roberto A. Foglietta" <roberto.foglietta@gmail.com>]

# uzpexec

https://github.com/robang74/gzcmd.sh/blob/main/README.md#uzpexec

> [!NOTE]
>
> Suggested file extension: **`.uzp`**

Utility for executing an ELF binary directly from stdin pipe:

- it runs binary via SSH/wget
- it runs gzip compressed binary
- it self-extract and execute

without writing it on the remote/local systems (memfd_create).

```sh
make clean tests
```

The [uzpexec](uzpexec.asm) (micro gzip pipe exec, written in
Assembler) replaces the previous `upexec` comparison which offers as
extra the integrated support for `gzip` inflate on the standard input
pipe. Pre-compiled v0.68 elf32 available
[here](https://github.com/robang74/working-in-progress/raw/refs/heads/main/uchaosys.qemu/uzpexec).

#### USAGE

-  `{ cat uzpexec; gzip -7c $elf; }    > $elf.uzp`
-  `cp uzpexec $elf.uzp; gzip -c $elf >> $elf.uzp`
-  `wget $url/$elf[.gz] -O- | uzpexec [args]`

It works as a single block 512-bytes self-inflating executable payload
replacing also `gzcmd.sh` with the sole requirement of `/bin/zcat`
available.

---

### Quick customisations

Quick customisations by `sed` and other stings-based editor is supported:

- `{ cat uzpexec | sed 's/zcat\x00/xzcat/'; xz -7c $elf; } > $elf.uxp`

Alternative to `zcat` are `xzcat` for XZ compression, or `lzcat` for LZMA.

The alternatives that are natively compatible with `-f -` are fully supported.

```
; =====================================================================
; COMPACT DATA SECTION (Appended to code)
; =====================================================================
copy_vers:  db "(c) 2026 robang74 l.MIT v0.68 git.new/ttRvFBu", 0
; filename can be changed by sed up to 7 chars + ending \0
; zcat -f is cat when input isn't gzip, options up to -6c\0
; /bin/zcat can be changed by sed up to 31 chars + ending \0
; - for example: /usr/local/bin/xzcat is 20 chars + ending \0
; eof_strng helps to find the EOF, and where \0 padding starts
filename:   db "uzpexec", 0
zcat_path:  db "/bin/zcat",  0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0
force_arg:  db "-f",  0,0, 0,0,0,0
dash_arg:   db "-", 0,0,0, 0,0,0,0
eof_strng:  db "elf_eof", 0

; =====================================================================
; PADDING: Aligned exactly to 512 bytes (as per skip request)
; =====================================================================
file_end:                       ; Physical end of the binary file!
times (512 - ($ - $$)) db 0     ; Padding to 512 bytes for skip=1
```

Since `zcat` is a shell script, it can be changed to pair the input
with the proper decompressing tool. While a tiny `xcat` binary in ASM
would be much faster in properly pairing the matches.

Best regards,
-- 
Roberto A. Foglietta
+49.176.274.75.661
+39.349.33.30.697

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