CVE-2020-24977 - Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Severity

98%

Complexity

39%

Confidentiality

98%

GNOME project libxml2 v2.9.10 and earlier have a global Buffer Overflow vulnerability in xmlEncodeEntitiesInternal at libxml2/entities.c. The issue has been fixed in commit 8e7c20a1 (20910-GITv2.9.10-103-g8e7c20a1).

GNOME project libxml2 v2.9.10 and earlier have a global buffer over-read vulnerability in xmlEncodeEntitiesInternal at libxml2/entities.c. The issue has been fixed in commit 8e7c20a1 (20910-GITv2.9.10-103-g8e7c20a1).

CVSS 3.1 Base Score 9.8. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

CVSS 2.0 Base Score 7.5. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:P/A:P).

CVSS 3.1 Base Score 6.5. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L).

CVSS 2.0 Base Score 6.4. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:N/A:P).

Demo Examples

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CWE-120

The following code asks the user to enter their last name and then attempts to store the value entered in the last_name array.


               
scanf ("%s", last_name);

The problem with the code above is that it does not restrict or limit the size of the name entered by the user. If the user enters "Very_very_long_last_name" which is 24 characters long, then a buffer overflow will occur since the array can only hold 20 characters total.

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CWE-120

The following code attempts to create a local copy of a buffer to perform some manipulations to the data.


               
}
...

However, the programmer does not ensure that the size of the data pointed to by string will fit in the local buffer and blindly copies the data with the potentially dangerous strcpy() function. This may result in a buffer overflow condition if an attacker can influence the contents of the string parameter.

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CWE-120

The excerpt below calls the gets() function in C, which is inherently unsafe.


               
}
...

However, the programmer uses the function gets() which is inherently unsafe because it blindly copies all input from STDIN to the buffer without restricting how much is copied. This allows the user to provide a string that is larger than the buffer size, resulting in an overflow condition.

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CWE-120

In the following example, a server accepts connections from a client and processes the client request. After accepting a client connection, the program will obtain client information using the gethostbyaddr method, copy the hostname of the client that connected to a local variable and output the hostname of the client to a log file.


               
...
close(serversocket);
}
close(clientsocket);

However, the hostname of the client that connected may be longer than the allocated size for the local hostname variable. This will result in a buffer overflow when copying the client hostname to the local variable using the strcpy method.

Demo Examples

Out-of-bounds Read

CWE-125

In the following code, the method retrieves a value from an array at a specific array index location that is given as an input parameter to the method


               
}
return value;// check that the array index is less than the maximum// length of the array
value = array[index];// get the value at the specified index of the array
// if array index is invalid then output error message// and return value indicating error
value = -1;

However, this method only verifies that the given array index is less than the maximum length of the array but does not check for the minimum value (CWE-839). This will allow a negative value to be accepted as the input array index, which will result in a out of bounds read (CWE-125) and may allow access to sensitive memory. The input array index should be checked to verify that is within the maximum and minimum range required for the array (CWE-129). In this example the if statement should be modified to include a minimum range check, as shown below.


               
...// check that the array index is within the correct// range of values for the array

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