Re: VSFTPD Remote Heap Overrun (low severity)

[Ramon de C Valle <rcvalle () redhat com>]

> Hi Ramon,
> Frankly I didn't look into the possibility to exploit this
> vulnerability,
> so i do not know if it is easy or hard to exploit. As you outlined
> it is difficult, during your audit you did not manage to trigger a
> function pointer call? :> i guess not
I have not tried much, but I have not get ouside of glibc scope after the overflow within a controllable environment. 
In your video, It seems you overwrite the file structure used in __tzfile_read. Is this a constant and controllable 
behaviour?

> I am not much into exploiting heap based overruns in the old times
> fashion.
> BTW both freebsd and pure-ftpd load locale files (strace it and you
> will see) from /usr,
> these locale files are used for the ftp responses to make them
> written
> in international language.
> FreeBSD ftpd in junction with the locale files loading will SIGSEGV
> (EIP overwrite)
> due to a strcpy in locale responses in a special codepath. I did not
> find a way to exploit Pure-FTPD through this
> locale loading tough, because Pure-FTPD is very restrictive in many
> ways even
I have not looked this yet, I'll take a look as soon as I have some time. But thanks for the additional information.

> on response lines but there might be a vuln there too. (I dont
> remember if locale loading was only
> on FreeBSD or also on Linux or also in vsftpd, since the libc behaves
> very different in BSD/glibc/eglibc etc)
One important thing to note is in Fedora and RHEL, when running SELinux, vsftpd runs confined by default, and can be 
configured by the following booleans:

[rcvalle@localhost ~]$ getsebool -a | grep ftpd 
allow_ftpd_anon_write --> off
allow_ftpd_full_access --> off
allow_ftpd_use_cifs --> off
allow_ftpd_use_nfs --> off
ftpd_connect_db --> off

[...]

[rcvalle@localhost ~]$ 

And unless the boolean allow_ftpd_full_access is enabled, vsftpd may not be allowed to read this file by default. Could 
you cause this running the vsftpd installed from packages distributed with CentOS, Fedora, or RHEL? I'm copying Dan 
Walsh so he can comment on this.

> Regards,
Thanks for forwarding my message to the list. It seems that my Red Hat email address has not yet been approved. John, 
can you approve this email address please?


-- 
Ramon de C Valle / Red Hat Security Response Team

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