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An exploitable arbitrary write vulnerability exists in the open document format parser of the Atlantis Word Processor, version 3.2.7.2, while trying to null-terminate a string. A specially crafted document can allow an attacker to pass an untrusted value as a length to a constructor. This constructor will miscalculate a length and then use it to calculate the position to write a null byte. This can allow an attacker to corrupt memory, which can result in code execution under the context of the application. An attacker must convince a victim to open a specially crafted document in order to trigger this vulnerability.
An exploitable arbitrary write vulnerability exists in the open document format parser of the Atlantis Word Processor, version 3.2.7.2, while trying to null-terminate a string. A specially crafted document can allow an attacker to pass an untrusted value as a length to a constructor. This constructor will miscalculate a length and then use it to calculate the position to write a null byte. This can allow an attacker to corrupt memory, which can result in code execution under the context of the application. An attacker must convince a victim to open a specially crafted document in order to trigger this vulnerability.
CVSS 3.0 Base Score 7.8. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H).
CVSS 2.0 Base Score 6.8. CVSS Attack Vector: network. CVSS Attack Complexity: medium. CVSS Vector: (AV:N/AC:M/Au:N/C:P/I:P/A:P).
The classic example of a write-what-where condition occurs when the accounting information for memory allocations is overwritten in a particular fashion. Here is an example of potentially vulnerable code:
}free(buf2);Vulnerability in this case is dependent on memory layout. The call to strcpy() can be used to write past the end of buf1, and, with a typical layout, can overwrite the accounting information that the system keeps for buf2 when it is allocated. Note that if the allocation header for buf2 can be overwritten, buf2 itself can be overwritten as well.
The allocation header will generally keep a linked list of memory "chunks". Particularly, there may be a "previous" chunk and a "next" chunk. Here, the previous chunk for buf2 will probably be buf1, and the next chunk may be null. When the free() occurs, most memory allocators will rewrite the linked list using data from buf2. Particularly, the "next" chunk for buf1 will be updated and the "previous" chunk for any subsequent chunk will be updated. The attacker can insert a memory address for the "next" chunk and a value to write into that memory address for the "previous" chunk.
This could be used to overwrite a function pointer that gets dereferenced later, replacing it with a memory address that the attacker has legitimate access to, where they have placed malicious code, resulting in arbitrary code execution.
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