CWE-831 与多个信号关联的信号处理例程

Signal Handler Function Associated with Multiple Signals

结构: Simple

Abstraction: Base

状态: Incomplete

被利用可能性: unkown

基本描述

The software defines a function that is used as a handler for more than one signal.

扩展描述

While sometimes intentional and safe, when the same function is used to handle multiple signals, a race condition could occur if the function uses any state outside of its local declaration, such as global variables or non-reentrant functions, or has any side effects.

An attacker could send one signal that invokes the handler function; in many OSes, this will typically prevent the same signal from invoking the handler again, at least until the handler function has completed execution. However, the attacker could then send a different signal that is associated with the same handler function. This could interrupt the original handler function while it is still executing. If there is shared state, then the state could be corrupted. This can lead to a variety of potential consequences depending on context, including denial of service and code execution.

Another rarely-explored possibility arises when the signal handler is only designed to be executed once (if at all). By sending multiple signals, an attacker could invoke the function more than once. This may generate extra, unintended side effects. A race condition might not even be necessary; the attacker could send one signal, wait until it is handled, then send the other signal.

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 364 cwe_View_ID: 1000 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 364 cwe_View_ID: 699 cwe_Ordinal: Primary

常见的影响

范围 影响 注释
['Availability', 'Integrity', 'Confidentiality', 'Access Control', 'Other'] ['DoS: Crash, Exit, or Restart', 'Execute Unauthorized Code or Commands', 'Read Application Data', 'Gain Privileges or Assume Identity', 'Bypass Protection Mechanism', 'Varies by Context'] The most common consequence will be a corruption of the state of the software, possibly leading to a crash or exit. However, if the signal handler is operating on state variables for security relevant libraries or protection mechanisms, the consequences can be far more severe, including protection mechanism bypass, privilege escalation, or information exposure.

示例代码

例

This code registers the same signal handler function with two different signals.

bad C

void handler (int sigNum) {
...
}

int main (int argc, char* argv[]) {
signal(SIGUSR1, handler)
signal(SIGUSR2, handler)
}

例

This code registers the same signal handler function with two different signals (CWE-831). If those signals are sent to the process, the handler creates a log message (specified in the first argument to the program) and exits.

bad C

char logMessage;

void handler (int sigNum) {
syslog(LOG_NOTICE, "%s\n", logMessage);
free(logMessage);
/ artificially increase the size of the timing window to make demonstration of this weakness easier. /

sleep(10);
exit(0);
}

int main (int argc, char argv[]) {
logMessage = strdup(argv[1]);
/ Register signal handlers. /

signal(SIGHUP, handler);
signal(SIGTERM, handler);
/ artificially increase the size of the timing window to make demonstration of this weakness easier. /

sleep(10);
}

The handler function uses global state (globalVar and logMessage), and it can be called by both the SIGHUP and SIGTERM signals. An attack scenario might follow these lines:

None

At this point, the state of the heap is uncertain, because malloc is still modifying the metadata for the heap; the metadata might be in an inconsistent state. The SIGTERM-handler call to free() is assuming that the metadata is inconsistent, possibly causing it to write data to the wrong location while managing the heap. The result is memory corruption, which could lead to a crash or even code execution, depending on the circumstances under which the code is running.

Note that this is an adaptation of a classic example as originally presented by Michal Zalewski [REF-360]; the original example was shown to be exploitable for code execution.

Also note that the strdup(argv[1]) call contains a potential buffer over-read (CWE-126) if the program is called without any arguments, because argc would be 0, and argv[1] would point outside the bounds of the array.

引用