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CloudFront 對 POODLE 的安全性更新

CloudFront 的進一步更新出來了,剛剛看到信件通知。分成兩種 case,一種是使用 dedicated IP 服務的人,一種是使用 *.cloudfront.net 的人。

使用 dedicated IP 的人仍然可以打開 SSLv3,不過 CloudFront 建議在 use case 允許下不要開:

If you are using the Dedicated IP Custom SSL Certificates to serve SSL traffic, you may configure whether your distribution accepts SSLv3 connections. We have added an option to select this in both the console and the API. For existing distributions that use Dedicated IP Custom SSL, the default value for this new setting will be to allow SSLv3, so you will need to update your distributions if you want to disallow SSLv3. We do recommend that customers disable SSLv3 if their use case allows it.

使用 *.cloudfront.net 預定在 2014/11/03 之後就會關閉 SSLv3:

Additionally, starting on November 3rd, 2014, we will begin disabling SSLv3 for ALL customers who use SSL with the default CloudFront domain name (*.cloudfront.net). If you believe that this policy will negatively affect your website or application, please contact us as soon as possible so that we can discuss your options: https://aws.amazon.com/forms/poodle_sslv3

而使用 SNI 的人不需要管這件事情,因為這代表你已經是用 TLS 了:

If you're using Custom SSL Certificates and Server Name Indication (SNI), you don’t need to take any action because, as SNI-Only Custom SSL distributions already did not allow SSLv3 connections.

SSL 3.0 爆炸,CVE-2014-3566,POODLE

這次的慘案是由 Google 的人找到 SSL 3.0 的問題:「This POODLE bites: exploiting the SSL 3.0 fallback」。

Google 提供的解法有兩種。一種是關掉 SSL 3.0,另外一種是關掉 SSL 3.0 的 CBC-mode cipher,但兩種解法都還是會痛:

Disabling SSL 3.0 support, or CBC-mode ciphers with SSL 3.0, is sufficient to mitigate this issue, but presents significant compatibility problems, even today.

提到相容性問題的原因是 Windows XP + IE6 的組合,在預設安裝下是不支援 TLS 1.0 的 (需要另外打開選項啟用),而看到那個 11.1%:


出自「Internet Explorer - IE 6 Countdown | Modern.IE

另外是 SSL 3.0 如果不支援 CBC-mode cipher 的話,也只剩下 RC4,而這早就千窗百孔了:


出自「Transport Layer Security

也因此,在 CBC-mode cipher 與 RC4 都不能用的情況下,CloudFlare 決定直接關閉 SSL 3.0:「SSLv3 Support Disabled By Default Due to POODLE Vulnerability」。

而其他廠商提供的方案也都差不多,像是 AWS 的「CVE-2014-3566 Advisory」裡建議的解法也是關閉 SSL 3.0:

This includes disabling SSLv3 on both server and client implementations.

新推出的 security policy (ELBSecurityPolicy-2014-10) 裡也直接關掉 SSL 3.0,讓真的有需要的人再手動加上去,或是選擇一月的版本。

SSL 3.0 推出 18 年後總算要被殲滅了...

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