Fix byte/string extraction and unit tests #1339
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capa/features/extractors/viv/insn.py
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| @@ -271,7 +271,7 @@ def extract_insn_bytes_features(fh: FunctionHandle, bb, ih: InsnHandle) -> Itera | |||
| if capa.features.extractors.helpers.all_zeros(buf): | |||
| continue | |||
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| if f.vw.isProbablyString(v): | |||
| if f.vw.isProbablyString(v) or f.vw.detectUnicode(v): | |||
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Suggested change
| if f.vw.isProbablyString(v) or f.vw.detectUnicode(v): | |
| if f.vw.isProbablyString(v) or f.vw.isProbablyUnicode(v): |
tests/fixtures.py
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| # don't extract byte features for obvious strings | ||
| ("mimikatz", "function=0x40105D", capa.features.common.Bytes("SCardControl".encode("utf-16le")), False), | ||
| ("mimikatz", "function=0x40105D", capa.features.common.String("SCardControl"), True), | ||
| ("mimikatz", "function=0x40105D", capa.features.common.Bytes("SCardTransmit".encode("utf-16le")), False), | ||
| ("mimikatz", "function=0x40105D", capa.features.common.Bytes("ACR > ".encode("utf-16le")), False), | ||
| ("mimikatz", "function=0x40105D", capa.features.common.String("ACR > "), True), |
williballenthin
approved these changes
Mar 1, 2023
mr-tz
commented
Mar 1, 2023
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| if vw.isProbablyString(p) or vw.isProbablyUnicode(p): | ||
| # don't deref strings that coincidentally are pointers | ||
| return |
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e.g. ACS... which would be 0x430041 (valid pointer) as seen in mimikatz at 0x493E30
mr-tz
commented
Mar 1, 2023
tests/fixtures.py
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| ("mimikatz", "function=0x401517", capa.features.common.Bytes(binascii.unhexlify("CA3B0E000000F8AF47")), True), | ||
| ("mimikatz", "function=0x404414", capa.features.common.Bytes(binascii.unhexlify("0180000040EA4700")), True), |
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must test True features here!
|
Tests in IDA succeed. |
|
Thanks a lot @xusheng6! |
Glad to help! |
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This PR fixes some unit tests that wrongly treat strings features as bytes features. It also fixes a bug in the IDA extractor that causes the old unit test to pass.
closes #1336 #1327
ref: #1338
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