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A flaw was found in xorg-x11-server before 1.20.10. A heap-buffer overflow in XkbSetDeviceInfo may lead to a privilege escalation vulnerability. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
CVSS 3.1 Base Score 7.8. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).
CVSS 2.0 Base Score 4.6. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (AV:L/AC:L/Au:N/C:P/I:P/A:P).
While buffer overflow examples can be rather complex, it is possible to have very simple, yet still exploitable, heap-based buffer overflows:
}strcpy(buf, argv[1]);The buffer is allocated heap memory with a fixed size, but there is no guarantee the string in argv[1] will not exceed this size and cause an overflow.
This example applies an encoding procedure to an input string and stores it into a buffer.
}
return dst_buf;die("user string too long, die evil hacker!");
else dst_buf[dst_index++] = user_supplied_string[i];dst_buf[dst_index++] = ';';
/* encode to < */The programmer attempts to encode the ampersand character in the user-controlled string, however the length of the string is validated before the encoding procedure is applied. Furthermore, the programmer assumes encoding expansion will only expand a given character by a factor of 4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure expands the string it is possible to overflow the destination buffer if the attacker provides a string of many ampersands.
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