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Re: RealVNC 4.1.2 minor heap corruption/DoS vulnerability (authentication required)
From: Juha-Matti Laurio <juha-matti.laurio () netti fi>
Date: Mon, 21 Aug 2006 02:41:39 +0300 (EEST)
They probably will post patch information here:
Niall FitzGibbon <fitzgibbon () blueyonder co uk> wrote:
This vulnerability affects the latest version of RealVNC (4.1.2) on all
platforms. It is tested on Windows.
To exploit the vulnerability, the attacker must either control a connected and
authenticated client connected to a vulnerable VNC server or control a VNC
server with at least one vulnerable connected and authenticated client.
The attack exploits a signed/unsigned integer mismatch leading to an integer
overflow and subsequent allocation of very large or zero size areas on the
heap. The result of the attack is Denial of Service due to heap corruption
and improper program flow. It doesn't seem possible to exploit the heap
corruption in order to gain code execution the source of the copy operation
is not defined by the attacker. The attack is thus of limited usefulness due
to the necessity of prior authentication.
The vulnerability lies in the following functions:
rfb/SMsgReader.cxx : readClientCutText()
rfb/CMsgReader.cxx : readServerCutText()
These functions handle clipboard changes propagated from the other party. The
simplest way to trigger this vulnerability is to modify the
CMsgWriter::clientCutText or SMsgWriter::writeServerCutText in order to send
an integer length of -1 on clipboard updates. This results in an allocation
of zero bytes to the heap on the other party and subsequent write of a zero
terminator to an address immediately before the allocated zero-length buffer
followed by a large memcpy to that buffer. When an exception is finally
thrown, RealVNC handles this by terminating the connection and possibly the
process, throwing an error message about the message type.
Reported to vendor (v4bugs () realvnc com) 01 August 2006. No response at time
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- Re: RealVNC 4.1.2 minor heap corruption/DoS vulnerability (authentication required) Juha-Matti Laurio (Aug 21)