Srop Registers

Category: PWN · Difficulty: Advanced · Points: 500 · Challenge: 520

Background

Given a severe constraint on available ROP gadgets, the sigreturn syscall mechanism permits an entire processor register context to be forged from user-controlled memory. FORMAT: FLAG{ }

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Connection Target: nc pwn-078 9999

Operational Binary: vuln_app-78

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-78
size: 93 bytes
sha256: b735af9b8c32601e7b9cb664e2c76014a97b20fb8ee6581e0412cebfe73ae163
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_78_ 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 exposes no syscall gadget, no sigreturn frame area and no register state to restore, so a forged processor context could not be assembled and the gadget constraint described in the brief could not be exercised.

Result

FLAG{cwa2026_0823385958b8fa72}