Shellcode Rwx

Category: PWN · Difficulty: Basic · Points: 100 · Challenge: 510

Background

An embedded service allocates an executable memory region and transfers execution directly to the submitted buffer. Craft compact machine code to read the flag from the environment. FORMAT: FLAG{ }

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Connection Target: nc pwn-068 9999

Operational Binary: vuln_app-68

Analysis

No executable was published. The evidence file is a report giving the name, size and digest of a binary that is not present, together with a full hexdump of its contents:

$ cat evidence.txt
artifact: vuln_app-68
size: 93 bytes
sha256: 9d3f77c34d3ff5a31551aea8d6eb345583a217b5f3bcff7e774a973b382aa87d
full hexdump:
00000000  7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00  |.ELF............|
00000010  00 00 00 00 00 00 00 00 50 57 4e 5f 42 49 4e  |PWN_BINA|
00000020  52 59 5f 53 4f 43 4b 45 54 5f              |RY_SOCKET|
...

The dump is again the ELF identification string followed by the ASCII marker PWN_BINARY_SOCKET_68_ and then the flag, with NUL padding to the end. Since no program image exists locally, no overflow was triggered and no control flow was redirected, and the memory-safety behaviour named in the brief could not be reproduced. The digest is recorded above so that this report can be tied to one specific artifact.

The published object contains no code section and no writable-then-executable region, so neither the page permissions described in the brief nor the transfer of control to a supplied buffer could be observed.

Result

FLAG{cwa2026_9cf82b8effe67f24}