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Re: Bug#991971: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances)
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From: Salvatore Bonaccorso <carnil () debian org>
Date: Sat, 7 Aug 2021 20:17:31 +0200
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Hi Axel,
On Sat, Aug 07, 2021 at 03:51:07AM +0200, Axel Beckert wrote:
Hi,
On Fri, Aug 06, 2021 at 05:14:32PM +0000, Thorsten Glaser
<tg () mirbsd de> wrote in
https://lists.nongnu.org/archive/html/lynx-dev/2021-08/msg00000.html:
this affects both OpenSSL and Debian’s nonGNUtls builds:
lynx https://user:pass@host/
… will lead to…
SSL error:host(user:pass@host)!=cert(CN<mainhost>:SAN<DNS=host>:SAN<DNS=otherhost>
… for OpenSSL lynx and…
SSL error:host(user:pass@host)!=cert(CN<mainhost>)-Continue? (n)
… for nonGNUtls lynx.
Obviously, user:pass@ need to be stripped before comparing.
This is more severe than it initially looked like: Due to TLS Server
Name Indication (SNI) the hostname as parsed by Lynx (i.e with
"user:pass@" included) is sent in _clear_ text over the wire even
_before_ I can even said "n" for "no, don't continue to talk with this
server" in Lynx's prompt as shown above.
I was able to capture the password given on the commandline in traffic
of an TLS handshake using tcpdump and analysing it with Wireshark:
From Wiresharks TLS dissector:
Server Name Indication extension
Server Name list length: 28
Server Name Type: host_name (0)
Server Name length: 25
Server Name: user:pass () www example org
^^^^^^^^^^
From Wiresharks "Follow TCP stream":
...........a
....jV.. ......../.......D.&....R.+.,..... .
.../.0...............z.{./.5.A...
.....|.}.3.9.E.............2.8.D.......p............$."...user:pass () www example org......#...
...
.................
..............................
(PCAPs available on request. Actually did the test with a local server
of mine. But it should be easy to reproduce, be it with any Linux
distribution.)
I did this test with Lynx from Debian Experimental (which has the
current Lynx upstream release 2.9.0dev.8) as well as with Lynx from
Debian 8 Jessie ELTS (which has Lynx 2.8.9dev.1) and both leak the
password via SNI. I though assume that older releases of Lynx are
probably also affected as well, at least if they or the according
crypto libraries support SNI.
But given that the symptoms Thorsten discovered stayed unreported for
quite some years, I assume that this use case is a rather seldom one.
Nevertheless only trying to use Lynx that way (and seeing it fail)
already leaks the used password.
IMHO this nevertheless needs a CVE-ID.
MITRE did assign CVE-2021-38165. MITRE raised the question: Does
2.9.0dev.9 (mentioned on the
https://lynx.invisible-island.net/current/CHANGES.html page) fix the
entire problem?
https://www.openwall.com/lists/oss-security/2021/08/07/7 claims that
credentials appear in the HTTP Host header to an http:// (i.e.,
non-SSL) website.
Regards,
Salvatore
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Current thread:
Re: bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances), (continued)
Re: bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Axel Beckert (Aug 07)
Re: bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Thorsten Glaser (Aug 07)
Re: Re: bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Stuart Henderson (Aug 07)
SNI is a security vulnerability all by itself (was Re: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances)) Thorsten Glaser (Aug 07)
Re: SNI is a security vulnerability all by itself (was Re: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances)) Jeffrey Walton (Aug 07)
Re: Re: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Ariadne Conill (Aug 07)
Re: [Lynx-dev] [oss-security] Re: bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Thorsten Glaser (Aug 07)
Re: Re: Bug#991971: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Axel Beckert (Aug 07)
Re: Re: Bug#991971: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Ariadne Conill (Aug 07)
Re: Re: Bug#991971: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Axel Beckert (Aug 07)
Re: Bug#991971: [Lynx-dev] bug in Lynx' SSL certificate validation -> leaks password in clear text via SNI (under some circumstances) Salvatore Bonaccorso (Aug 07)
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