Michal Trojnara reports:
A buffer overflow vulnerability due to incorrect integer conversion in the NTLM authentication of the CONNECT protocol negotiation
The vulnerability is exploitable under the following conditions:
-Stunnel versions 4.21 until 4.54.
-Stunnel compiled as a 64-bit executable. Any 32-bit builds, including pre-compiled Win32 binaries, are not vulnerable.
-Service configured in SSL client mode ("client = yes").
-CONNECT protocol negotiation enabled ("protocol = connect").
-NTLM authentication enabled ("protocolAuthentication = NTLM").
-The attacker able either to control the proxy server specified as a parameter of the "connect" option, or to perform MITM attacks on TCP sessions between stunnel and the proxy server.
The vulnerability may be exploited for arbitrary code execution. The code is executed within the configured chroot directory, with privileges of the configured user and group.
Upgrade to stunnel 4.55, or disable the NTLM authentication.
Vulnerability discovery: Mateusz Kocielski, LogicalTrust
(In reply to comment #0)
> Upgrade to stunnel 4.55, or disable the NTLM authentication.
This issue does NOT affect the versions of the stunnel package, as shipped with Fedora release of 17 and 18 - the stunnel-4.55-1.fc17 and stunnel-4.55-1.fc18 versions (which contain the fix for this issue) has been pushed to particular Fedora release -testing repository already:
This issue has been addressed in following products:
Red Hat Enterprise Linux 6
Via RHSA-2013:0714 https://rhn.redhat.com/errata/RHSA-2013-0714.html
This issue did not affect the version of the stunnel package as shipped with Red Hat Enterprise Linux 5.