ICU Heap / Integer Overflows

2015.05.06
Credit: Pedro Ribeiro
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-189

tl;dr heap and integer overflows in ICU, many packages affected, unknown if these can be exploited or not - everyone names vulns nowadays, so I name these I-C-U-FAIL. Hi, I have found two vulnerabilities in the ICU library while fuzzing LibreOffice, full details in the advisory below. Disclosure of these was done initially to LibreOffice and then to distro-security. I then reported it to Chromium, Android and finally CERT, so I ended up breaking the rules of distro-security which requires that any vulnerability reported to the list is made public in 14 days. I apologise for this to oss-security, distro-security and Solar Designer, and will not do it again. A full copy of the advisory below can be found in my repo at https://raw.githubusercontent.com/pedrib/PoC/master/generic/i-c-u-fail.txt. Regards, Pedro >> Heap overflow and integer overflow in ICU library >> Discovered by Pedro Ribeiro (pedrib@gmail.com), Agile Information Security ================================================================================= Disclosure: 04/05/2015 / Last updated: 04/05/2015 >> Background on the affected products: ICU is a mature, widely used set of C/C++ and Java libraries providing Unicode and Globalization support for software applications. ICU is widely portable and gives applications the same results on all platforms and between C/C++ and Java software. >> Summary: While fuzzing LibreOffice an integer overflow and a heap overflow where found in the ICU library. This library is used by LibreOffice and hundreds of other software packages. Proof of concept files can be downloaded from [1]. These files have been tested with LibreOffice 4.3.3.2 and LibreOffice 4.4.0-beta2 and ICU 52. Note that at this point in time it is unknown whether these vulnerabilities are exploitable. Thanks to CERT [2] for helping disclose these vulnerabilities. >> Technical details: #1 Vulnerability: Heap overflow CVE-2014-8146 The code to blame is the following (from ubidi.c:2148 in ICU 52): dirProp=dirProps[limit-1]; if((dirProp==LRI || dirProp==RLI) && limit<pBiDi->length) { pBiDi->isolateCount++; pBiDi->isolates[pBiDi->isolateCount].stateImp=stateImp; pBiDi->isolates[pBiDi->isolateCount].state=levState.state; pBiDi->isolates[pBiDi->isolateCount].start1=start1; } else processPropertySeq(pBiDi, &levState, eor, limit, limit); Under certain conditions, isolateCount is incremented too many times, which results in several out of bounds writes. See [1] for a more detailed analysis. #2 Vulnerability: Integer overflow CVE-2014-8147 The overflow is on the resolveImplicitLevels function (ubidi.c:2248): pBiDi->isolates[pBiDi->isolateCount].state=levState.state; pBiDi->isolates[].state is a int16, while levState.state is a int32. The overflow causes an error when performing a malloc on pBiDi->insertPoints->points because insertPoints is adjacent in memory to isolates[]. The Isolate struct is defined in ubidiimp.h:184 typedef struct Isolate { int32_t startON; int32_t start1; int16_t stateImp; int16_t state; } Isolate; LevState is defined in ubidi.c:1748 typedef struct { const ImpTab * pImpTab; /* level table pointer */ const ImpAct * pImpAct; /* action map array */ int32_t startON; /* start of ON sequence */ int32_t startL2EN; /* start of level 2 sequence */ int32_t lastStrongRTL; /* index of last found R or AL */ int32_t state; /* current state */ int32_t runStart; /* start position of the run */ UBiDiLevel runLevel; /* run level before implicit solving */ } LevState; >> Fix: The ICU versions that are confirmed to be affected are 52 to 54, but earlier versions might also be affected. Upgrade to ICU 55.1 to fix these vulnerabilities. Note that there are probably many other software packages that embed the ICU code and will probably also need to be updated. >> References: [1] https://github.com/pedrib/PoC/raw/master/generic/i-c-u-fail.7z [2] https://www.kb.cert.org/vuls/id/602540

References:

https://github.com/pedrib/PoC/raw/master/generic/i-c-u-fail.7z
https://raw.githubusercontent.com/pedrib/PoC/master/generic/i-c-u-fail.txt


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