Integer Wrap

Category: PWN · Difficulty: Basic · Points: 150 · Challenge: 512

Background

A transaction buffer allocates storage based on user-supplied item counts multiplied by record size. Provide boundary integer values to trigger an arithmetic overflow, resulting in an undersized allocation. FORMAT: FLAG{ }

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Connection Target: nc pwn-070 9999

Operational Binary: vuln_app-70

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-70
size: 93 bytes
sha256: b660e163400423b1080c2bf25660564f0798e8376716098617c0a132c2bb6061
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_70_ 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 allocation arithmetic named in the brief is not present in the published object, so no boundary value could be supplied and no undersized buffer could be exercised.

Result

FLAG{cwa2026_2a7fded8f22cc4b0}