CVE-2021-39597 - NULL Pointer Dereference







An issue was discovered in swftools through 20200710. A NULL pointer dereference exists in the function code_dump2() located in code.c. It allows an attacker to cause Denial of Service.

CVSS 3.1 Base Score 5.5. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H).

CVSS 2.0 Base Score 4.3. CVSS Attack Vector: network. CVSS Attack Complexity: medium. CVSS Vector: (AV:N/AC:M/Au:N/C:N/I:N/A:P).

Demo Examples

NULL Pointer Dereference


While there are no complete fixes aside from conscientious programming, the following steps will go a long way to ensure that NULL pointer dereferences do not occur.

/* make use of pointer1 *//* ... */

If you are working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished.

NULL Pointer Dereference


This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

strcpy(hostname, hp->h_name);/*routine that ensures user_supplied_addr is in the right format for conversion */

If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference would then occur in the call to strcpy().

Note that this example is also vulnerable to a buffer overflow (see CWE-119).

NULL Pointer Dereference


In the following code, the programmer assumes that the system always has a property named "cmd" defined. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method.

cmd = cmd.trim();

NULL Pointer Dereference


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.


First reported 1 month ago

2021-09-20 16:15:00

Last updated 1 month ago

2021-09-22 18:15:00

Affected Software


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