Introduction to Ngrep

    Date10 Jan 2003
    4443
    Posted ByAnthony Pell
    During the source of investigating the wu-ftpd exploit (see references), analysts were reminded of the one of the limitations of current Intrusion Detection Systems; the inability to handle regular expressions. When the attack has identifiable fixed strings of characters, the signature . . .
    During the source of investigating the wu-ftpd exploit (see references), analysts were reminded of the one of the limitations of current Intrusion Detection Systems; the inability to handle regular expressions. When the attack has identifiable fixed strings of characters, the signature is reasonably straightforward.

    The problem comes when we don't have a fixed series of characters to match against. The November 2001 wu-ftpd exploit used the fact that a sequence of whitespace, a tilde, optional characters, a left curly brace, and any other characters without a matching right curly brace would crash wu-ftpd, allowing a buffer overflow exploit to take over.

    Because of the possibility of additional characters and the requirement that the second block of characters not contain a "}", we need to use something stronger than fixed strings.

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