COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONMITRE canlı kaydı

CAPEC-53

Postfix, Null Terminate, and Backslash

If a string is passed through a filter of some kind, then a terminal NULL may not be valid. Using alternate representation of NULL allows an adversary to embed the NULL mid-string while postfixing the proper data so that the filter is avoided. One example is a filter that looks for a trailing slash character. If a string insertion is possible, but the slash must exist, an alternate encoding of NULL in mid-string may be used.

Soyutlama

Detailed

Tipik ciddiyet

High

Saldırı ihtimali

High

Saldırıyı anla

Bu saldırı kalıbı nedir?

If a string is passed through a filter of some kind, then a terminal NULL may not be valid. Using alternate representation of NULL allows an adversary to embed the NULL mid-string while postfixing the proper data so that the filter is avoided. One example is a filter that looks for a trailing slash character. If a string insertion is possible, but the slash must exist, an alternate encoding of NULL in mid-string may be used.

Uygulama akışı

Saldırı adım adım nasıl ilerler?

1

Explore

Survey the application for user-controllable inputs

Using a browser, an automated tool or by inspecting the application, an adversary records all entry points to the application.

Kullanılan teknikler

  • Use a spidering tool to follow and record all links and analyze the web pages to find entry points. Make special note of any links that include parameters in the URL.
  • Use a proxy tool to record all user input entry points visited during a manual traversal of the web application.
  • Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery.
  • Manually inspect the application to find entry points.
2

Experiment

Probe entry points to locate vulnerabilities

The adversary uses the entry points gathered in the "Explore" phase as a target list and injects postfix null byte(s) followed by a backslash to observe how the application handles them as input. The adversary is looking for areas where user input is placed in the middle of a string, and the null byte causes the application to stop processing the string at the end of the user input.

Kullanılan teknikler

  • Try different encodings for null such as \0 or %00 followed by an encoding for the backslash character.
3

Exploit

Remove data after null byte(s)

After determined entry points that are vulnerable, the adversary places a null byte(s) followed by a backslash such that they bypass an input filter and remove data after the null byte(s) in a way that is beneficial to them.

Kullanılan teknikler

  • If the input is a directory as part of a longer file path, add a null byte(s) followed by a backslash at the end of the input to try to traverse to the given directory.

Gereksinimler

Saldırının gerçekleşmesi için ne gerekir?

Ön koşullar

  • Null terminators are not properly handled by the filter.

Gerekli beceri

  • Medium: An adversary needs to understand alternate encodings, what the filter looks for and the data format acceptable to the target API

Gerekli kaynak

MITRE kaydında belirtilmemiş.

Tespit

Saldırının göstergeleri nelerdir?

Null characters are observed by the filter. The filter needs to be able to understand various encodings of the Null character, or only canonical data should be passed to it.

Etki

Başarılı saldırı neye yol açar?

Modify Data

Etkilenen alanlar: Integrity

Read Data

Etkilenen alanlar: Confidentiality

Gain Privileges

Etkilenen alanlar: Confidentiality, Access Control, Authorization

Savunma

Nasıl önlenir ve etkisi azaltılır?

1
Properly handle Null characters. Make sure canonicalization is properly applied. Do not pass Null characters to the underlying APIs.
2
Assume all input is malicious. Create an allowlist that defines all valid input to the software system based on the requirements specifications. Input that does not match against the allowlist should not be permitted to enter into the system.

Gerçek dünya

MITRE örnek olayları

Örnek olay 1Detay
A rather simple injection is possible in a URL: http://getAccessHostname/sekbin/ helpwin.gas.bat?mode=&draw=x&file=x&module=&locale=[insert relative path here] [%00][%5C]&chapter= This attack has appeared with regularity in the wild. There are many variations of this kind of attack. Spending a short amount of time injecting against Web applications will usually result in a new exploit being discovered.