Signal Handler Use of a Non-reentrant Function

Opis

The product defines a signal handler that calls a non-reentrant function.

Non-reentrant functions are functions that cannot safely be called, interrupted, and then recalled before the first call has finished without resulting in memory corruption. This can lead to an unexpected system state and unpredictable results with a variety of potential consequences depending on context, including denial of service and code execution.

Many functions are not reentrant, but some of them can result in the corruption of memory if they are used in a signal handler. The function call syslog() is an example of this. In order to perform its functionality, it allocates a small amount of memory as "scratch space." If syslog() is suspended by a signal call and the signal handler calls syslog(), the memory used by both of these functions enters an undefined, and possibly, exploitable state. Implementations of malloc() and free() manage metadata in global structures in order to track which memory is allocated versus which memory is available, but they are non-reentrant. Simultaneous calls to these functions can cause corruption of the metadata.

Skutki

• Integrity, Confidentiality, Availability

  Execute Unauthorized Code or Commands

  It may be possible to execute arbitrary code through the use of a write-what-where condition.

• Integrity

  Modify Memory; Modify Application Data

  Signal race conditions often result in data corruption.

Zapobieganie

• Requirements

  Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness.

• Architecture and Design

  Design signal handlers to only set flags rather than perform complex functionality.

• Implementation

  Ensure that non-reentrant functions are not found in signal handlers.

• Implementation

  Use sanity checks to reduce the timing window for exploitation of race conditions. This is only a partial solution, since many attacks might fail, but other attacks still might work within the narrower window, even accidentally.

  Skuteczność: Defense in Depth

Przykłady podatności

• CVE-2005-0893 signal handler calls function that ultimately uses malloc()
• CVE-2004-2259 SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.

Słabość nadrzędna

• CWE-828 Signal Handler with Functionality that is not Asynchronous-Safe
• CWE-663 Use of a Non-reentrant Function in a Concurrent Context

Może prowadzić do

• CWE-123 Write-what-where Condition

Kiedy powstaje

• Implementation

Dotyczy

C, C++

Źródła

1. The CLASP Application Security Process — Secure Software, Inc., 2005
2. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 13, "Signal Vulnerabilities", Page 791, Addison Wesley, 2006