Hanno's blog

Lately a lot of attention has been payed to software like Superfish and Privdog that intercepts TLS connections to be able to manipulate HTTPS traffic. These programs had severe (technically different) vulnerabilities that allowed attacks on HTTPS connections.

What these tools do is a widespread method. They install a root certificate into the user's browser and then they perform a so-called Man in the Middle attack. They present the user a certificate generated on the fly and manage the connection to HTTPS servers themselves. Superfish and Privdog did this in an obviously wrong way, Superfish by using the same root certificate on all installations and Privdog by just accepting every invalid certificate from web pages. What about other software that also does MitM interception of HTTPS traffic?

Antivirus software intercepts your HTTPS traffic

Many Antivirus applications and other security products use similar techniques to intercept HTTPS traffic. I had a closer look at three of them: Avast, Kaspersky and ESET. Avast enables TLS interception by default. By default Kaspersky intercepts connections to certain web pages (e. g. banking), there is an option to enable interception by default. In ESET TLS interception is generally disabled by default and can be enabled with an option.

When a security product intercepts HTTPS traffic it is itself responsible to create a TLS connection and check the certificate of a web page. It has to do what otherwise a browser would do. There has been a lot of debate and progress in the way TLS is done in the past years. A number of vulnerabilities in TLS (upon them BEAST, CRIME, Lucky Thirteen, FREAK and others) allowed to learn much more how to do TLS in a secure way. Also, problems with certificate authorities that issued malicious certificates (Diginotar, Comodo, Türktrust and others) led to the development of mitigation technologies like HTTP Public Key Pinning (HPKP) and Certificate Transparency to strengthen the security of Certificate Authorities. Modern browsers protect users much better from various threats than browsers used several years ago.

You may think: "Of course security products like Antivirus applications are fully aware of these developments and do TLS and certificate validation in the best way possible. After all security is their business, so they have to get it right." Unfortunately that's only what's happening in some fantasy IT security world that only exists in the minds of people that listened to industry PR too much. The real world is a bit different: All Antivirus applications I checked lower the security of TLS connections in one way or another.

Disabling of HTTP Public Key Pinning

Each and every TLS intercepting application I tested breaks HTTP Public Key Pinning (HPKP). It is a technology that a lot of people in the IT security community are pretty excited about: It allows a web page to pin public keys of certificates in a browser. On subsequent visits the browser will only accept certificates with these keys. It is a very effective protection against malicious or hacked certificate authorities issuing rogue certificates.

Browsers made a compromise when introducing HPKP. They won't enable the feature for manually installed certificates. The reason for that is simple (although I don't like it): If they hadn't done that they would've broken all TLS interception software like these Antivirus applications. But the applications could do the HPKP checking themselves. They just don't do it.

Kaspersky vulnerable to FREAK and CRIME

Having a look at Kaspersky, I saw that it is vulnerable to the FREAK attack, a vulnerability in several TLS libraries that was found recently. Even worse: It seems this issue has been reported publicly in the Kaspersky Forums more than a month ago and it is not fixed yet. Please remember: Kaspersky enables the HTTPS interception by default for sites it considers as especially sensitive, for example banking web pages. Doing that with a known security issue is extremely irresponsible.

I also found a number of other issues. ESET doesn't support TLS 1.2 and therefore uses a less secure encryption algorithm. Avast and ESET don't support OCSP stapling. Kaspersky enables the insecure TLS compression feature that will make a user vulnerable to the CRIME attack. Both Avast and Kaspersky accept nonsensical parameters for Diffie Hellman key exchanges with a size of 8 bit. Avast is especially interesting because it bundles the Google Chrome browser. It installs a browser with advanced HTTPS features and lowers its security right away.

These TLS features are all things that current versions of Chrome and Firefox get right. If you use them in combination with one of these Antivirus applications you lower the security of HTTPS connections.

There's one more interesting thing: Both Kaspersky and Avast don't intercept traffic when Extended Validation (EV) certificates are used. Extended Validation certificates are the ones that show you a green bar in the address line of the browser with the company name. The reason why they do so is obvious: Using the interception certificate would remove the green bar which users might notice and find worrying. The message the Antivirus companies are sending seems clear: If you want to deliver malware from a web page you should buy an Extended Validation certificate.

Everyone gets HTTPS interception wrong - just don't do it

So what do we make out of this? A lot of software products intercept HTTPS traffic (antiviruses, adware, youth protection filters, ...), many of them promise more security and everyone gets it wrong.

I think these technologies are a misguided approach. The problem is not that they make mistakes in implementing these technologies, I think the idea is wrong from the start. Man in the Middle used to be a description of an attack technique. It seems strange that it turned into something people consider a legitimate security technology. Filtering should happen on the endpoint or not at all. Browsers do a lot these days to make your HTTPS connections more secure. Please don't mess with that.

I question the value of Antivirus software in a very general sense, I think it's an approach that has very fundamental problems in itself and often causes more harm than good. But at the very least they should try not to harm other working security mechanisms.

(You may also want to read this EFF blog post: Dear Software Vendors: Please Stop Trying to Intercept Your Customers’ Encrypted Traffic)

Two days ago, the german Chaos Computer Club (CCC) published a sample that's supposedly a variant of a german state spy software (the so-called "Bundestrojaner").

You might wonder if your anti virus software is protecting you. The webpage Virus Total lets you upload suspicious files, scans them with 43 different anti virus applications and presents you the result. Currently, 24 of 43 scanners detect the Bundestrojaner.

The CCC provides some further information where they state that the file they released is not the original one - they had several samples that differed and to avoid detection of the potential source, they changed the differing parts to something completely else. You might wonder if your anti virus app also detects the "original" Bundestrojaner and not just the modified file the CCC released.

We can easily check this if we change the modified pieces again to something else. A modified variant lowered the detection rate to 14 of 43 - amongst them the popular McAffee software. Now, it's pretty useless to only detect the exact published sample of a malware if we know that the original malware is different.

Application	Version	Sig date	Modified sample	Original CCC sample
AhnLab-V3	2011.10.08.01	2011-Okt-09	Trojan/Win32.R2d2	Trojan/Win32.R2d2
AntiVir	7.11.15.175	2011-Okt-09	TR/GruenFink.1	TR/GruenFink.1
Antiy-AVL	2.0.3.7	2011-Okt-09	-	-
Avast	6.0.1289.0	2011-Okt-09	Win32:Trojan-gen	Win32:Trojan-gen
AVG	10.0.0.1190	2011-Okt-07	-	-
BitDefender	7.2	2011-Okt-10	Backdoor.R2D2.A	Backdoor.R2D2.A
ByteHero	1.0.0.1	2011-Sep-23	-	-
CAT-QuickHeal	11.00	2011-Okt-07	-	-
ClamAV	0.97.0.0	2011-Okt-10	Trojan.BTroj-1	Trojan.BTroj-1
Commtouch	5.3.2.6	2011-Okt-10	-	W32/R2D2.A
Comodo	10407	2011-Okt-10	-	Backdoor.Win32.R2D2.A
DrWeb	5.0.2.03300	2011-Okt-10	-	-
Emsisoft	5.1.0.11	2011-Okt-10	Trojan.Win32.Bundestrojaner!A2	Backdoor.Win32.R2D2!IK
eSafe	7.0.17.0	2011-Okt-06	-	-
eTrust-Vet	36.1.8605	2011-Okt-07	-	-
F-Prot	4.6.2.117	2011-Okt-09	-	W32/R2D2.A
F-Secure	9.0.16440.0	2011-Okt-10	Backdoor:W32/R2D2.A	Backdoor:W32/R2D2.A
Fortinet	4.3.370.0	2011-Okt-10	-	W32/R2D2.A!tr.bdr
GData	22	2011-Okt-10	Backdoor.R2D2.A	Backdoor.R2D2.A
Ikarus	T3.1.1.107.0	2011-Okt-10	-	Backdoor.Win32.R2D2
Jiangmin	13.0.900	2011-Okt-09	-	-
K7AntiVirus	91155258	2011-Okt-08	-	-
Kaspersky	9.0.0.837	2011-Okt-09	Backdoor.Win32.R2D2.a	Backdoor.Win32.R2D2.a
McAfee	5.400.0.1158	2011-Okt-10	-	Artemis!930712416770
McAfee-GW-Edition	2010.1D	2011-Okt-09	-	Artemis!930712416770
Microsoft	17702	2011-Okt-10	Backdoor:Win32/R2d2.A	Backdoor:Win32/R2d2.A
NOD32	6529	2011-Okt-10	Win32/R2D2.A	Win32/R2D2.A
Norman	6.7.2011	2011-Okt-09	-	-
nProtect	2011-10-10.01	2011-Okt-10	-	-
Panda	10.0.3.5	2011-Okt-09	-	Suspiciousfile
PCTools	8.0.0.5	2011-Okt-10	Backdoor.R2D2	Backdoor.R2D2
Prevx	3.0	2011-Okt-10	-	-
Rising	23.78.06.02	2011-Okt-09	-	-
Sophos	4.70.0	2011-Okt-10	Troj/BckR2D2-A	Troj/BckR2D2-A
SUPERAntiSpyware	4.40.0.1006	2011-Okt-08	-	-
Symantec	20111.2.0.82	2011-Okt-10	Backdoor.R2D2	Backdoor.R2D2
TheHacker	6.7.0.1.318	2011-Okt-09	-	-
TrendMicro	9.500.0.1008	2011-Okt-09	-	-
TrendMicro-HouseCall	9.500.0.1008	2011-Okt-10	-	BKDR_R2D2.A
VBA32	3.12.16.4	2011-Okt-07	-	-
VIPRE	10718	2011-Okt-10	-	Trojan.Win32.Generic!BT
ViRobot	2011.10.10.4710	2011-Okt-10	-	-
VirusBuster	14.1.3.0	2011-Okt-09	-	-

Scans done Monday morning around 8:00.