Détail du CAPEC-67

This attack targets applications and software that uses the syslog() function insecurely. If an application does not explicitely use a format string parameter in a call to syslog(), user input can be placed in the format string parameter leading to a format string injection attack. Adversaries can then inject malicious format string commands into the function call leading to a buffer overflow. There are many reported software vulnerabilities with the root cause being a misuse of the syslog() function.

Flux d'exécution

[Identify target application] The adversary identifies a target application or program to perform the buffer overflow on. In this attack, adversaries look for applications that use syslog() incorrectly.

[Find injection vector] The adversary identifies an injection vector to deliver the excessive content to the targeted application's buffer. For each user-controllable input that the adversary suspects is vulnerable to format string injection, attempt to inject formatting characters such as %n, %s, etc.. The goal is to manipulate the string creation using these formatting characters.

• Inject probe payload which contains formatting characters (%s, %d, %n, etc.) through input parameters.

[Craft overflow content] The adversary crafts the content to be injected. If the intent is to simply cause the software to crash, the content need only consist of an excessive quantity of random data. If the intent is to leverage the overflow for execution of arbitrary code, the adversary will craft a set of content that not only overflows the targeted buffer but does so in such a way that the overwritten return address is replaced with one of the adversaries' choosing which points to code injected by the adversary.

• The formatting characters %s and %d are useful for observing memory and trying to print memory addresses. If an adversary has access to the log being written to they can observer this output and use it to help craft their attack.
• The formatting character %n is useful for adding extra data onto the buffer.

[Overflow the buffer] Using the injection vector, the adversary supplies the program with the crafted format string injection, causing a buffer.

Conditions préalables

The Syslog function is used without specifying a format string argument, allowing user input to be placed direct into the function call as a format string.

Atténuations

Array

Faiblesses connexes

Références

REF-1

Exploiting Software: How to Break Code
G. Hoglund, G. McGraw.

REF-503

Exploiting Format String Vulnerabilities
scut, team teso.
http://doc.bughunter.net/format-string/exploit-fs.html

REF-504

Auditing binaries for security vulnerabilities
Halvar Flake.
http://www.blackhat.com/presentations/bh-europe-00/HalvarFlake/HalvarFlake.ppt

REF-505

Fortify Taxonomy of Vulnerabilities
https://vulncat.hpefod.com/en

REF-506

Syslog man page
http://www.rt.com/man/syslog.3.html

Soumission

Modifications