Category Archives: Broken Encryption

How to: Secure Chrome against Logjam

Update: Chrome 45 was released on 9/1/15 with a fix for the “logjam” vulnerability.  Use Chrome 45 or newer

Disable the following cipher suites

  • (0xcc15) TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256
  • (0xcc9e) TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
  • (0x0039) TLS_DHE_RSA_WITH_AES_256_CBC_SHA
  • (0x0033) TLS_DHE_RSA_WITH_AES_128_CBC_SHA

Until the Chrome 45 update, the easiest by far is to

Step 1:
Modify an existing (or create) a shortcut to Chrome.  Right click on the shortcut and select Properties

Step 2:
Add the following to the application Target:

It should look like this:
(Note: Target field is long and is split into two screenshots)

20150530-secure-chrome-logjam-step2-1

20150530-secure-chrome-logjam-step2

Step 3:
Click Apply or OK to save

Step 4:
Close all Chrome browser windows

Step 5:
Use the shortcut you just modified to re-open Chrome and verify these cipher suites have been disabled

Quick: https://weakdh.org/

20150605-secure-chrome-logjam-weakdh.org-step5

Detailed: https://www.ssllabs.com/ssltest/viewMyClient.html

(h/t) @eckes on twitter: https://twitter.com/eckes/status/604090760032559104

 

Reference

The fix is “on track to be included in Chrome 45”

 

Downloads

I zipped the Logjam safe shortcut from this tutorial.

If you used the standard installer your application path is %UserProfile%\AppData\Local\Google\Chrome\Application\chrome.exe

Download “Windows Default 32-bit Chrome (Logjam Safe) Shortcut” Google-Chrome-Logjam-Safe.zip – Downloaded 61 times – 1 KB

Google Chrome (Logjam Safe).lnk

  • MD5: 32D2342D138B66A3F458D66842038CA5
  • SHA1: CAB26DCFEF880D5D7422633A2732770CB6B0BB17

If you used the “offline installer” Chrome installs to “C:\Program Files (x86)\Google\Chrome\Application\chrome.exe”

Download “"Program Files (x86)" 32-bit Chrome (Logjam Safe) Shortcut” Chrome (Logjam Safe).lnk.zip – Downloaded 50 times – 1 KB

Chrome (Logjam Safe).lnk

  • MD5: C689CABE8887CD8187CAAFA395DBCF2B
  • SHA1: EE2E1D54BA3DF586406BB13CA3E35E41A130745B

Original content and screenshots on this page are licensed under a Creative Commons Attribution 3.0 License (http://creativecommons.org/licenses/by/3.0/us/)

How to: Secure Firefox against Logjam

Update: Firefox 39 was released on 7/2/15 with a fix for the logjam vulnerability (advisory on “logjam”). Use Firefox 39 or newer

Disable the following:

  • security.ssl3.dhe_rsa_aes_128_sha
  • security.ssl3.dhe_rsa_aes_256_sha

following are step by step instructions

How to: Secure Firefox against Logjam (until Firefox 39 is released)

Step 1:
Type “about:config” in the navigation bar

20150530-secure-firefox-logjam-step1

 

Step 2:
Continue through the warning screen by clicking “I’ll be careful, I promise!”

20150530-secure-firefox-logjam-step2

 

Step 3:
Search for “ssl3”

20150530-secure-firefox-logjam-step3

 

Step 4:
Disable the following (by double clicking or right clicking then “Toggle”)  Changes are saved automatically

  • security.ssl3.dhe_rsa_aes_128_sha
  • security.ssl3.dhe_rsa_aes_256_sha

20150530-secure-firefox-logjam-step4

 

Step 5:
Verify these cipher suites have been disabled

Quick: https://weakdh.org/

Before

20150530-secure-firefox-logjam-step0

After

20150530-secure-firefox-logjam-step5

 

Detailed: https://www.ssllabs.com/ssltest/viewMyClient.html

20150530-secure-firefox-logjam-ssltest-before

20150530-secure-firefox-logjam-ssltest-after

 

(h/t) http://techdows.com/2015/05/how-to-make-firefox-browser-safe-against-logjam-attack.html

Additional Information

Mozilla released (5/22/15) an add-on that changes these settings – https://addons.mozilla.org/mk/firefox/addon/disable-dhe/

Per Mozilla – Firefox 39 will include changes that will increase the minimum strength of keys to 1024 bits.

20150530-firefox-39

 

Content from Qualys licensed under a Creative Commons Attribution 3.0 License (http://creativecommons.org/licenses/by/3.0/us/).   Arrows and Before and After tags were added to screenshots of the original content.

Original content and screenshots on this page are licensed under a Creative Commons Attribution 3.0 License (http://creativecommons.org/licenses/by/3.0/us/)

Your browser is still vulnerable to Logjam

Currently, only Internet Explorer is safe from the Logjam vulnerability.

How to: Secure Chrome against Logjam

How to: Secure Firefox against Logjam

Browser/OS Windows OS X iOS Android
IE 11 Safe
(5/20/15 CW)
Safari Vulnerable
(5/20/15 CW)
Vulnerable
(5/20/15 CW)
Chrome 43 Vulnerable
(5/25/15 SOT)
Vulnerable
(5/20/15 CW)
Vulnerable
(5/20/15 CW)
Vulnerable
(5/20/15 CW)
Firefox 38 Vulnerable
(5/30/15 SOT)
Vulnerable
(5/20/15 CW)
Vulnerable
(5/20/15 CW)
Android browser Vulnerable
(5/20/15 CW)

This article builds upon the information in the Computerworld (CW) article published 5/20/15

Test your client (browser):

Patches / Safe Versions

5/12/15 – Microsoft patched IE 11 see MS15-055

5/22/15 – Mozilla released the “Disable DHE” add-on that “disables ephemeral Diffie-Hellman cipher suites that are vulnerable to the logjam attack” for Firefox versions 20.0 – 38.*

 

SOT Testing

5/25/15 – Firefox 38.0.1

20150525-firefox-38-0-1-up-to-date

20150525-ssllabs.com-ssl-client-test-logjam-firefox-38-vulnerable

2015052-ssllabs.com-manual-tetst-firefox-38-vulnerable

5/30/15 – Firefox 38.0.1 no updated release – still vulnerable

Additional information

Schannel – Secure Channel

The Logjam Attack

Last updated: 12/15/15

Official website

https://weakdh.org/

Twitter hashtags

Vulnerability testing tools

Test your browser (client):

Test your server:

 

Vulnerable browser results

If your browser is vulnerable you will see:

weakdh.org Vulnerable web browser example

20150524-weakdh.org-vulnerable-browser
weakdh.org: Warning! Your web browser is vulnerable to Logjam and can be tricked into using weak encryption. You should update your browser.

 

Qualys SSL Labs client test Vulnerable user agent example

20150524-ssllabs.com-ssl-client-test-logjam-vulnerability
ssllabs.com: Your user agent is vulnerable. Upgrade as soon as possible.

 

Qualys SSL Labs manual Logjam Vulnerability test Vulnerable example

20150524-ssllabs.com-vulnerable-user-agent
ssllabs.com: Your user agent is vulnerable to the Logjam attack

 

Vulnerable server results

If the server tested is vulnerable you will see:

weakdh.org Vulnerable server – uses a commonly-shared 1024-bit Diffie-Hellman group

20150524-weakdh.org-vulnerable-server
weakdh.org: Warning! This site uses a commonly-shared 1024-bit Diffie-Hellman group, and might be in range of being broken by a nation-state. It might be a good idea to generate a unique, 2048-bit group for the site.

 

Safe client results

If your browser is safe you will see:

weakdh.org Safe web browser

20150530-secure-firefox-logjam-step5
Good News! Your browser is safe against the Logjam attack.

 

Safe server results

Two examples of safe server results below:

weakdh.org Safe – uses 2048-bit Diffie-Hellman group

20150524-weakdh.org-safe-server
weakdh.org: Good News! This site uses strong (2048-bit or better) key exchange parameters and is safe from the Logjam attack.

 

weakdh.org Safe – does not use DHE

20150524-weakdh.org-whitehouse.gov-safe-server
weakdh.org: Good News! This site is safe from the Logjam attack. It supports ECDHE and does not use DHE.

 

Secure your browser and server

 

Logjam timeline

Upcoming

Interesting reads

 

Additional information

Terms (in order of appearance):

  • DHE – Ephemeral Diffie-Hellman (also commonly referred to as EDH)
  • ECDHE – Elliptic Curve Ephemeral Diffie-Hellman

Content licensing

Content from Qualys licensed under a Creative Commons Attribution 3.0 License (http://creativecommons.org/licenses/by/3.0/us/).  No changes were made to the original content.


Creating this post

Jing was used for screenshots and WP Smush was used to remove PNG metadata.