i-c-u-fail.txt

>> Heap overflow and integer overflow in ICU library (v52 to v54)
>> Discovered by Pedro Ribeiro (pedrib@gmail.com), Agile Information Security
=================================================================================
Disclosure: 04/05/2015 / Last updated: 07/05/2015

>> 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 were 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: 
All ICU releases between 52 and 54 are affected. Upgrade to ICU 55.1 to fix these vulnerabilities.
There are many other software packages which embed the ICU code and will need to be updated.
Patches that fix these vulnerabilities can be obtained from the ICU project in [3] and [4].


>> References:
[1] https://github.com/pedrib/PoC/raw/master/generic/i-c-u-fail.7z
[2] https://www.kb.cert.org/vuls/id/602540
[3] http://bugs.icu-project.org/trac/changeset/37080
[4] http://bugs.icu-project.org/trac/changeset/37162


================
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