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It was discovered systemd does not correctly check the content of PIDFile files before using it to kill processes. When a service is run from an unprivileged user (e.g. User field set in the service file), a local attacker who is able to write to the PIDFile of the mentioned service may use this flaw to trick systemd into killing other services and/or privileged processes. Versions before v237 are vulnerable.
It was discovered systemd does not correctly check the content of PIDFile files before using it to kill processes. When a service is run from an unprivileged user (e.g. User field set in the service file), a local attacker who is able to write to the PIDFile of the mentioned service may use this flaw to trick systemd into killing other services and/or privileged processes. Versions before v237 are vulnerable.
CVSS 3.0 Base Score 4.7. CVSS Attack Vector: local. CVSS Attack Complexity: high. CVSS Vector: (CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H).
CVSS 2.0 Base Score 1.9. CVSS Attack Vector: local. CVSS Attack Complexity: medium. CVSS Vector: (AV:L/AC:M/Au:N/C:N/I:N/A:P).
The following code sets the umask of the process to 0 before creating a file and writing "Hello world" into the file.
}/* Ignore CWE-59 (link following) for brevity */fclose(out);After running this program on a UNIX system, running the "ls -l" command might return the following output:
-rw-rw-rw- 1 username 13 Nov 24 17:58 hello.outThe "rw-rw-rw-" string indicates that the owner, group, and world (all users) can read the file and write to it.
This code creates a home directory for a new user, and makes that user the owner of the directory. If the new directory cannot be owned by the user, the directory is deleted.
}return true;return false;return false;Because the optional "mode" argument is omitted from the call to mkdir(), the directory is created with the default permissions 0777. Simply setting the new user as the owner of the directory does not explicitly change the permissions of the directory, leaving it with the default. This default allows any user to read and write to the directory, allowing an attack on the user's files. The code also fails to change the owner group of the directory, which may result in access by unexpected groups.
This code may also be vulnerable to Path Traversal (CWE-22) attacks if an attacker supplies a non alphanumeric username.
The following code snippet might be used as a monitor to periodically record whether a web site is alive. To ensure that the file can always be modified, the code uses chmod() to make the file world-writable.
close($outFH);chmod 0777, $fileName;ExitError("Couldn't append to $fileName: $!");The first time the program runs, it might create a new file that inherits the permissions from its environment. A file listing might look like:
-rw-r--r-- 1 username 13 Nov 24 17:58 secretFile.outThis listing might occur when the user has a default umask of 022, which is a common setting. Depending on the nature of the file, the user might not have intended to make it readable by everyone on the system.
The next time the program runs, however - and all subsequent executions - the chmod will set the file's permissions so that the owner, group, and world (all users) can read the file and write to it:
-rw-rw-rw- 1 username 13 Nov 24 17:58 secretFile.outPerhaps the programmer tried to do this because a different process uses different permissions that might prevent the file from being updated.
The following command recursively sets world-readable permissions for a directory and all of its children:
chmod -R ugo+r DIRNAMEIf this command is run from a program, the person calling the program might not expect that all the files under the directory will be world-readable. If the directory is expected to contain private data, this could become a security problem.
This example demonstrates a shopping interaction in which the user is free to specify the quantity of items to be purchased and a total is calculated.
...The user has no control over the price variable, however the code does not prevent a negative value from being specified for quantity. If an attacker were to provide a negative value, then the user would have their account credited instead of debited.
This example asks the user for a height and width of an m X n game board with a maximum dimension of 100 squares.
.../* board dimensions */die("No integer passed: Die evil hacker!\n");die("No integer passed: Die evil hacker!\n");die("Value too large: Die evil hacker!\n");While this code checks to make sure the user cannot specify large, positive integers and consume too much memory, it does not check for negative values supplied by the user. As a result, an attacker can perform a resource consumption (CWE-400) attack against this program by specifying two, large negative values that will not overflow, resulting in a very large memory allocation (CWE-789) and possibly a system crash. Alternatively, an attacker can provide very large negative values which will cause an integer overflow (CWE-190) and unexpected behavior will follow depending on how the values are treated in the remainder of the program.
The following example shows a PHP application in which the programmer attempts to display a user's birthday and homepage.
echo "Birthday: $birthday<br>Homepage: <a href=$homepage>click here</a>"The programmer intended for $birthday to be in a date format and $homepage to be a valid URL. However, since the values are derived from an HTTP request, if an attacker can trick a victim into clicking a crafted URL with <script> tags providing the values for birthday and / or homepage, then the script will run on the client's browser when the web server echoes the content. Notice that even if the programmer were to defend the $birthday variable by restricting input to integers and dashes, it would still be possible for an attacker to provide a string of the form:
2009-01-09--If this data were used in a SQL statement, it would treat the remainder of the statement as a comment. The comment could disable other security-related logic in the statement. In this case, encoding combined with input validation would be a more useful protection mechanism.
Furthermore, an XSS (CWE-79) attack or SQL injection (CWE-89) are just a few of the potential consequences when input validation is not used. Depending on the context of the code, CRLF Injection (CWE-93), Argument Injection (CWE-88), or Command Injection (CWE-77) may also be possible.
This function attempts to extract a pair of numbers from a user-supplied string.
}
die("Did not specify integer value. Die evil hacker!\n");/* proceed assuming n and m are initialized correctly */This code attempts to extract two integer values out of a formatted, user-supplied input. However, if an attacker were to provide an input of the form:
123:then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).
The following example takes a user-supplied value to allocate an array of objects and then operates on the array.
}list[0] = new Widget();die("Negative value supplied for list size, die evil hacker!");This example attempts to build a list from a user-specified value, and even checks to ensure a non-negative value is supplied. If, however, a 0 value is provided, the code will build an array of size 0 and then try to store a new Widget in the first location, causing an exception to be thrown.
This application has registered to handle a URL when sent an intent:
}......
}
}int length = URL.length();...The application assumes the URL will always be included in the intent. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called.
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