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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=763 The LZMA specification says the following about the memory usage of decompression: "The size of the probability model counter arrays is calculated with the following formula: size_of_prob_arrays = 1846 + 768 * (1 << (lp + lc))" But that formula only holds true if you keep the parameters within the specified range, which the SDK gives as: lp - The number of literal pos bits (low bits of current position for literals). It can be in the range from 0 to 4. The default value is 0. lc - The number of literal context bits (high bits of previous literal). It can be in the range from 0 to 8. The default value is 3. If you set the parameters outside those ranges, then the rest of the assumptions don't hold and memory corruption can occur. Comodo do not attempt to keep these parameters in range, and lots of memory corruption can occur, the attached testcase should crash during an LZMA decode operation by overflowing a heap buffer. This vulnerability is obviously exploitable for remote code execution as NT AUTHORITY\SYSTEM. (438.dd4): Access violation - code c0000005 (first chance) First chance exceptions are reported before any exception handling. This exception may be expected and handled. unpack!CreateInstance+0x654bc: 000007fe<code>f29890cc 66f3abrep stos word ptr [rdi] 0:010> r rax=0000000000000400 rbx=0000000000000000 rcx=000000007ffffe88 rdx=0000000000000001 rsi=000000000b154588 rdi=000000000bbfc000 rip=000007fef29890cc rsp=000000000d6cd2c0 rbp=0000000000000000 r8=0000000000023c7cr9=000000000d6cd378 r10=0000000000000001 r11=000000000b361000 r12=0000000000000001 r13=000000000b39c38c r14=0000000000000000 r15=000000000bbfaea4 iopl=0 nv up ei ng nz na po nc cs=0033ss=002bds=002bes=002bfs=0053gs=002b efl=00010286 unpack!CreateInstance+0x654bc: 000007fe</code>f29890cc 66f3abrep stos word ptr [rdi] This is trying to initialize the probabilities array, but overflowing the heap buffer allocated and running off a page boundary. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39602.zip |
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