I have an ELF file and want to know if it is UPX packed. How can I detect UPX compression in GNU/Linux?
4 Answers
Okay, assuming vanilla UPX you should be fine by detecting the strings UPX!
or UPX0
. As far as I remember this would also work on Windows.
So it's a shell one-liner such as:
grep UPX\! <filename>
or
grep UPX0 <filename>
... assuming the GNU version of grep
here.
Another method, but using the same principle:
$ hexdump -C <filename> |grep -C 1 UPX
000000a0 00 00 00 00 00 00 00 00 00 00 20 00 00 00 00 00 |.......... .....|
000000b0 c3 af e9 18 55 50 58 21 20 08 0d 16 00 00 00 00 |....UPX! .......|
000000c0 a0 fd 16 00 a0 fd 16 00 38 02 00 00 c6 00 00 00 |........8.......|
--
0000cf60 fe 61 03 83 78 b5 54 03 67 8b 85 2d ca a8 12 3c |.a..x.T.g..-...<|
0000cf70 44 ad bc 12 ab 7e 86 55 50 58 30 0e 01 ee 7c 64 |D....~.UPX0...|d|
0000cf80 00 f7 d1 80 4a 11 03 58 6e ac 0d 01 ff 92 83 e8 |....J..Xn.......|
--
000544e0 73 20 66 69 6c 65 20 69 73 20 70 61 63 6b 65 64 |s file is packed|
000544f0 20 77 69 74 68 20 74 68 65 20 55 50 58 20 65 78 | with the UPX ex|
00054500 65 63 75 74 61 62 6c 65 20 70 61 63 6b 65 72 20 |ecutable packer |
00054510 68 74 74 70 3a 2f 2f 75 70 78 2e 73 66 2e 6e 65 |http://upx.sf.ne|
00054520 74 20 24 0a 00 24 49 64 3a 20 55 50 58 20 33 2e |t $..$Id: UPX 3.|
00054530 30 38 20 43 6f 70 79 72 69 67 68 74 20 28 43 29 |08 Copyright (C)|
--
00054e40 7d 24 24 92 b7 0c 7f 12 01 a8 24 49 92 ff 00 00 |}$$.......$I....|
00054e50 00 00 55 50 58 21 00 00 00 00 00 00 55 50 58 21 |..UPX!......UPX!|
00054e60 0d 16 08 07 80 44 b5 80 b9 9a 8a d9 a0 08 00 00 |.....D..........|
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5
I do not recommend you to rely on the strings or section names you may find. Normally, it will indicate that the file is packed with UPX but, specially if you're analyzing malware, it may be done in order to fool you. My recommendation is to look to the entry point and find a pattern similar to this one:
0x00023b60 ; FUNCTION start
0x00023b60 (01) 60 PUSHA
0x00023b61 (05) be00904300 MOV ESI, 0xHARDCODED_VIRTUAL_ADDRESS
0x00023b66 (06) 8dbe0080fcff LEA EDI, [ESI-0x38000]
0x00023b6c (01) 57 PUSH EDI
0x00023b6d (02) eb0b JMP 0x00023b7a ; 1
Basically, find for PUSHA, MOV ESI, VIRTUAL_ADDRESS, LEA and JMP.
In Linux/Unix variants, strings command has helped me identify some of the packers such as UPX, Aspack, NSPack, NTKrnl, PeCompact, Themida, etc., All these packers tend to leave embedded strings in the packed executable which helps identify the type of packer. Granted, the author of the elf file could introduce the very same strings intentionally to throw your analysis off-track. I would just use this as a starting point in my analysis.
Here are some of the identification strings that helped me identify the packer type.
UPX - UPX0, UPX1, UPX2
Aspack - aspack, adata
NSPack - NSP0, NSP1, NSP2
NTKrnl - NTKrnl Security Suite
PECompact - PEC2, PECompact2
Themida - Themida, aPa2Wa
Also, the file command identifies some common packer formats too.
If you suspect that the file is definitely packed with UPX, then I would recommend the suggestion from 0xC0000022L.
- get UPX
- make your own UPX-packed ELFs, with different options (LZMA, NRV,...)
- As UPX is easy to modify, and very often modified, patched or even faked, comparing the code starts will make it easy to check if your target is indeed UPX-packed, and if this is truely the original UPX version or if it's modified in any way.
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That is actually an excellent point, but it makes it pretty tedious, because even the vanilla UPX has so many versions. Still +1– 0xC0000022L ♦Mar 26, 2013 at 20:06
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you're right but it's still manageable: vanilla UPX has a lot of versions, but they have little variation in their flow, so they're not byte-identical, but the structure is really similar. typically, a decent UPX hack has some extra code between major parts, like decompression and import loading. I re-uploaded an old commented UPX IDB of mine, maybe it will help.– AngeMar 27, 2013 at 7:56