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Google Chrome 對 WoSign 與 StartCom 的白名單要完全移除了

Twitter 上看到的:

WoSignStartCom 的移除會發生在 61 版,而依照「Final removal of trust in WoSign and StartCom Certificates」這邊的說明,stable 應該會在九月出 61 版而生效:

Based on the Chromium Development Calendar, this change should be visible in the Chrome Dev channel in the coming weeks, the Chrome Beta channel around late July 2017, and will be released to Stable around mid September 2017.

Google Chrome 也宣佈不信任 WoSign + StartCom 的計畫

Google Chrome 也公開了對 WoSign + StartCom 的計畫:「Distrusting WoSign and StartCom Certificates」。

由於大家遇到的技術問題都一樣 (之前發出的量太大,無法窮舉表列出來),所以處理的方法也類似於 Mozilla 的作法,只信任 2016/10/21 前發出的 certificate:

Beginning with Chrome 56, certificates issued by WoSign and StartCom after October 21, 2016 00:00:00 UTC will not be trusted.

Google Chrome 目前是 54,所以這表示會在兩個版本後生效。另外特別提出來必須有 CT flag (Certificate Transparency),或是在白名單的網站:

Certificates issued before this date may continue to be trusted, for a time, if they comply with the Certificate Transparency in Chrome policy or are issued to a limited set of domains known to be customers of WoSign and StartCom.

而因為安全考量,會有某些 certificate 是沒救的情況:(就上面的描述,看起來是指不在白名單內又沒標 CT flag 的)

Due to a number of technical limitations and concerns, Google Chrome is unable to trust all pre-existing certificates while ensuring our users are sufficiently protected from further misissuance.

話說 www.kernel.org 從本來的 StartCom 換掉了 (之前都要打 badidea 進去看),剛剛看是 2016/10/11 簽的憑證...

這樣除了 Microsoft 還是沒動作外,其他比較大的瀏覽器都到齊了...

Mozilla 對 WoSign + StartCom 的正式處分

MozillaWoSign + StartCom 的不信任處分出爐了:「Distrusting New WoSign and StartCom Certificates」,最後處分的內容跟之前的討論差不多 (參考先前寫的「Mozilla 對於 WoSign + StartCom 根憑證的新發展:拔除」)。

Mozilla 台灣有放出中文版的說明 (差不多就是英文翻譯的版本):「取消對 WoSign 與 StartCom 新簽發憑證的信任」。

這次比較麻煩的地方在於要信任已經發出的 certificate,而且量太大無法窮舉。所以必須改增加程式碼處理,而這個方法無法對使用 Mozilla CA Certificate Store 的人生效 (因為這包套件只是一堆 pem 檔案,沒辦法放特殊的邏輯進去...)

另外現在 Firefox 是 49 版,要到 51 版才會生效,看起來還會花一陣子...

Mozilla 對於 WoSign + StartCom 根憑證的新發展:拔除

Okay,在 Mozilla 的人跟 WoSign + StartCom + 360 的人談過後有了新的進展。

幾個小時前 Mozilla 提了新版的草案出來 (對,還是草案):「Remediation Plan for WoSign and StartCom」。但由於 Kathleen Wilson 跟 Gervase Markham 都沒有太多意見,我猜這應該會接近定案了。

這次的處分草案由 Kathleen Wilson 發出來,會包括這些 root certificate,可以看到包括了所有 WoSign 與 StartCom 的 CA:

1) Subject: CN=CA 沃通根证书, OU=null, O=WoSign CA Limited, C=CN
2) Subject: CN=Certification Authority of WoSign, OU=null, O=WoSign CA Limited, C=CN
3) Subject: CN=Certification Authority of WoSign G2, OU=null, O=WoSign CA Limited, C=CN
4) Subject: CN=CA WoSign ECC Root, OU=null, O=WoSign CA Limited, C=CN
5) Subject: CN=StartCom Certification Authority, OU=Secure Digital Certificate Signing, O=StartCom Ltd., C=IL
6) Subject: CN=StartCom Certification Authority, OU=Secure Digital Certificate Signing, O=StartCom Ltd., C=IL
7) Subject: CN=StartCom Certification Authority G2, OU=null, O=StartCom Ltd., C=IL

首先是認定這一連串的事件是惡意行為:

Based on the information that I have seen regarding WoSign, I believe that WoSign intentionally bent the rules in order to continue issuing SHA-1 SSL certs, when they knew full well that was no longer allowed. I also believe that the deception continued even after Mozilla directly asked WoSign about this. WoSign has lost my confidence in their ability and intention to follow Mozilla's policies.

所以打算採取與 CNNIC 類似的處分方法,但很不幸的由於規模不一樣,所以被迫採用另外的方式來處理:

Therefore, I think we should respond similarly to WoSign as we did to CNNIC [1][2]. Unfortunately, the number of certificates and the timescales involved are such that we prefer not to create a list of the domains for which previously-issued certs that chain up to the Affected Roots may continue to be trusted, so our approach will be a little different, as Gerv previously described[3].

這次處分的過程會包括四個項目,第一個是在 Firefox 51 會用黑名單的方式將這些 root certificate 擋下,但會信任 2016/10/21 前所發出的憑證以降低對目前網站的衝擊:

1) Distrust certificates chaining up to Affected Roots with a notBefore date after October 21, 2016. If additional back-dating is discovered (by any means) to circumvent this control, then Mozilla will immediately and permanently revoke trust in the Affected Roots.
-- This change will go into the Firefox 51 release train [4].
-- The code will use the subject key id (hash of public key) to identify the Affected Roots, so that the control will also apply to cross-certs of the Affected Roots.

然後將之前簽出來的 SHA-1 憑證列入 OneCRL:

2) Add the previously identified backdated SHA-1 certs chaining up to the Affected Roots to OneCRL.

另外一個非常大的事情是,Mozilla 將永久不信任安永香港的稽核報告:

3) No longer accept audits carried out by Ernst & Young Hong Kong.

Gervase Markham 做了補充「永久」的部份:

To be clear, this is a permanent ban, applicable worldwide, but only to the Hong Kong branch of E&Y. (If further issues are found with E&Y audits elsewhere, then we might consider something with wider scope.)

最後一個是移除 NSS 裡包的憑證:

4) Remove the Affected Roots from NSS after the SSL certificates issued before October 1, 2016, have expired or have been replaced.

在討論裡有提到 Firefox 與 NSS 的處置日期不太一樣的問題 (一個是 10/21,一個是 10/01),應該會在正式的定案時修正。

另外在「StartCom & Qihoo Incidents」這邊,Google 家的 Ryan Sleevi 也寫了一串,也許是他目前個人的看法 (但畢竟他是 Google 家主事的人之一),基本上的立場與 Mozilla 相同 (將 WoSign 與 StartCom 視為同一個單位,而且是刻意違反 Baseline Requirement),所以後續應該也會有動作了...

Comodo 取消對 WoSign CA 的 Cross-signed

剛剛看到 ComodoRob Stradling 在群組上說明了 Comodo 透過 CRLOCSP 取消對 WoSign CA 的 cross-signed:「Incidents involving the CA WoSign」。

Today we have revoked (via CRL and OCSP) all 3 of the cross-certificates that we'd issued to WoSign:

https://crt.sh/?id=3223853
https://crt.sh/?id=12716343
https://crt.sh/?id=12716433

See also:
https://bugzilla.mozilla.org/show_bug.cgi?id=906611#c2

然後另外也看到在倫敦與 Qihoo 360StartCom 以及 WoSign 的會面也已經結束了,接下來 Mozilla 會討論新的計畫後更新上來:「WoSign and StartCom: next steps」。

iOS 阻擋 WoSign 憑證

mozilla.dev.security.policy 上看到有人行動了:「Apple's response to the WoSign incidents」。這使得 Apple 成為 WoSign 事件中第一個行動的單位。

Apple 這次先把 WoSign 放入 iOS 憑證清單的黑名單公告在這邊:「Blocking Trust for WoSign CA Free SSL Certificate G2」。

WoSign 在 iOS 產品線中是靠 StartComComodo 的交叉簽章,所以如果 Apple 只想擋 WoSign 憑證的話,必須以阻擋 Intermediate CA 的方式避開:

Although no WoSign root is in the list of Apple trusted roots, this intermediate CA used cross-signed certificate relationships with StartCom and Comodo to establish trust on Apple products.

不過為了降低對 user 的影響,這次的阻擋會有例外。當 CT log server 在 2016-09-19 前收到的 SSL certificate 還是會信任 (要注意的重點是,這邊的日期不是簽發,是送到 CT log server 上):

To avoid disruption to existing WoSign certificate holders and to allow their transition to trusted roots, Apple products will trust individual existing certificates issued from this intermediate CA and published to public Certificate Transparency log servers by 2016-09-19.

接下來會開始更深入的調查 WoSign 與 StartCom:

As the investigation progresses, we will take further action on WoSign/StartCom trust anchors in Apple products as needed to protect users.

另外本來的棚子裡,Qihoo 360 與 StartCom 正式提出要求在 2016/10/04 與 Mozilla 的人面對面討論 (在英國):「WoSign and StartCom: next steps」:

Following the publication of the recent investigative report, representatives of Qihoo 360 and StartCom have requested a face-to-face meeting with Mozilla. We have accepted, and that meeting will take place next Tuesday in London.

繼續來看進度... 下個禮拜應該會有更多的資料出來。

Mozilla 對 WoSign 事件的決策 (草稿階段)

在「Mozilla 在考慮移除 WoSign 的 CA Root」這邊提到的事情,隨著時間的發展,大家發現事情愈來愈誇張。

在兩個小時前 MozillaGervase Markham 提出了對 WoSign + StartCom 處置的草稿:「WoSign and StartCom」,草稿在 Google Docs 上的「WoSign and StartCom」這邊可以看到。另外 Mozilla 在 wiki 上「CA:WoSign Issues」將 WoSign + StartCom 的事情都整理了出來,也是重要的資料。

文章很長,先講結論:目前 Mozilla 打算把 WoSign 與 StartCom 所簽出的 certificate 都照當年 CNNIC 的方式拔掉。

從頭說明,事情發生於八月底的時候 Google 通知了 Mozilla 一連串 WoSign 出包卻沒有主動通報的事件,當時知道的大約有三或四件。而在 mozilla.dev.security.policy 不斷的討論的情況下,由於關注度變得超高,在搜尋大量的資料下發現更多問題,到現在 Mozilla 的 wiki 上已經列出了 13 個。

而這邊以 Mozilla 最後整理的草稿,將 13 個事件整合起來成幾件來說明:

WoSign and Back-Dated SHA-1

在瀏覽器會對 2016 後所簽出直接跳 error 的情況下 (像是「An update on SHA-1 certificates in Chrome」),直接偽造是 2015 年簽出的 certificate。

WoSign’s Ownership of StartCom

Mozilla 的 CA program 要求當公司擁有權轉移時必須揭露:

[...], Mozilla’s program requirements say that a change of CA ownership must be disclosed. In this case, that was not done - and in fact, the change was directly denied a few months after it happened.

直到最近被抓到而揭露後,發現 WoSign 所揭露的也不正確,StartCom 已經開始使用 WoSign 的 infrastructure 了:

More recently, even after the evidence of total control was public, WoSign referred to their interest in StartCom in a press release as “an equity investment”, and maintain that the two businesses continue to be separate even today. They say “the original system ... of StartCom remains unchanged”.

However, there is technical evidence that around a month and a half after the acquisition, StartCom issuances switched to using WoSign’s infrastructure - either the same instance of it, or their own instance.

而 Mozilla 要求 WoSign 提供他們產生 serial number 的程式碼時:(在 WoSign 簽出重複的 serial number 問題時得到的)

Mozilla asked WoSign how they generated their serial numbers, and was told that they used the Java package java.crypto.SecureRandom. They supplied the following code snippet:

[...]

However, as can be seen from this simple test harness, this code snippet does not produce serial numbers matching WoSign’s idiosyncratic pattern.

再度發現 WoSign 給的程式碼對不上。(hey)

然後再多方面分析後發現 WoSign 宣稱跟 StartCom 只共用 CRL/OCSP (revoke 機制) 是假的。Mozilla 由多方面判斷發現,至少程式碼是共用的 (i.e. clone),甚至猜測整個系統都是共用的 (在更後面提到):

We believe that, taken together, all this shows that StartCom’s certificates are now being issued using either WoSign’s existing infrastructure or a clone of it, and that WoSign’s operational control of StartCom began straight after the November 1st 2015 sale date. This evidence should be compared against WoSign’s recent assertion that “Even now, it still independent in the system, in the validation team and management team, we share the CRL/OCSP distribution resource only.”

SHA-1 Exceptions Process

再來是講一些背景。因為金流產業到了 2016 年還是有系統不支援 SHA-256 certificate,而 CA/Browser Forum 已經禁止簽發 SHA-1 憑證了,所以 2016 年二月的時候 WorldPay 跑上來尋求例外:

This became clear in February of 2016, where a payment processor called WorldPay applied to the CAB Forum for an exception so they could acquire 8 SHA-1 certificates to keep SSL working for their legacy payment terminals. Their CA was unable to help them because of the ban in the CAB Forum Baseline Requirements, and to issue in violation of the ban would lead to a “qualified” (not clean) audit, which might lead to browsers no longer accepting their audit as valid to keep them trusted.

而在亞利桑那的 face-to-face meeting 中剛好就討論了這點,允許 Symantec 簽發,而要提出來的是,WoSign 的 Richard Wang 也在場:

This issue was discussed at length in the CAB Forum face-to-face meeting from 16th-18th February 2016 in Scottsdale, Arizona (where Richard Wang of WoSign was present). Mozilla then had a public discussion about it in our policy forum starting on 23rd of February. In the end, the browsers reluctantly agreed to let Symantec issue these certificates for Worldpay - or rather, they agreed to accept that Symantec’s next audit would be qualified in this way.

所以 Mozilla 再次強調,當下大家的結論是特別許可,簽發被禁止的 SHA-1 certificate 是很嚴重違反規定的事情:

Even at this point, in February 2016, it was (or should have been) clear to all CAs, including WoSign, that issuing SHA-1 certificates in violation of the ban was a Very Big Deal, and that permission had to be sought from the browsers in order for the CA not to face difficulty.

Tyro

接下來是 Tyro,這是一家澳洲金流廠商,直接複製草稿上的時間表:

Feb 3rd 2010GeoTrust issues a SHA-1 certificate for *.tyro.com from their Equifax root, valid until May 6th 2013.
Apr 6th 2013A month before their old cert expires, GeoTrust issues a replacement SHA-1 certificate for *.tyro.com from a GeoTrust root, valid until June 7th 2016. A simple roll-over replacement.
Jan 1st 2016SHA-1 issuance ban comes into effect.
May 24th 2016A month before their old cert expires, GeoTrust issues a SHA-256 certificate for *.tyro.com from a GeoTrust root, valid until June 23rd 2019.

但 Tyro 在 2016 年五月拿到的 SHA-256 憑證很明顯不合用,於是試著找 SHA-1 憑證... 結果不管怎樣,後來拿到了 StartCom 所簽出來的 SHA-1 憑證,而藉由技術上的 pattern 可以發現這是 back-dated (偽造日期簽發):

But the strong evidence is that this SHA-256 certificate did not meet Tyro’s needs. We can see a SHA-1 certificate for *.tyro.com which was logged in CT on June 8th 2016, a day after their previous SHA-1 certificate expired. This certificate is not issued by GeoTrust (who still provide the cert for their main website) or Comodo, tyro.com’s usual providers, but by StartCom. And the notBefore date is that magic date of 20th December, 2015 - a date on which, as noted above, StartSSL.com was closed for upgrading, and on which we have seen many Macau certificates issued by WoSign, which we believe are back-dated.

也可以很清楚的確認到現在還在使用:

The SHA-1 certificate in question is still in use today on https://iclient.tyro.com/.

Conculsions

最後 Mozilla 得到的結論:

  • StartCom are using WoSign’s infrastructure (the same or a clone);
  • Certificates on this infrastructure with a notBefore of 2015-12-20 (China time) are indeed back-dated - this further confirms our suspicions about the Macau certificates we saw issued by WoSign; and
  • StartCom’s hierarchy has been directed by management to mis-issue “WoSign-style”.

同時他們認為最後一點是最嚴重的一點,你必須將 StartCom 視為與 WoSign 完全同樣的公司,所有對 WoSign 的檢查與處置都必須相同對應到 StartCom 上:

This last point is important; the practices at WoSign are now being seen at StartCom. Therefore, we conclude that all of ownership, infrastructure and control are sufficiently common between the two companies that it would therefore be reasonable for any action Mozilla chooses to take against WoSign to also be taken against StartCom and vice versa.

另外一個很嚴肅的問題,CA 架構是建立在稽核機制上,而 WoSign 所選擇的稽核單位無法稽核出應有的「多個問題」:

WoSign’s auditors, Ernst & Young (Hong Kong), have failed to detect multiple issues they should have detected. (Issue J, Issue X)

提案的處理方式類似於 CNNIC 當時被拔掉的方式,針對某個日期之後的都不信任。這同時包括了 WoSign 與 StartCom 的 certificate。這真是可喜可賀啊...

在 Google Chrome 連上因 HSTS 而無法連線的網站

Update (2018/03/15):字串改了,請參考「本來 Google Chrome 要繞過 HSTS 的 badidea 被換掉了...」。

像是把 StartCom 停用掉後造成 www.kernel.org 無法連線的問題:

前幾天在 Twitter 上看到解法:

說道 StartCom,StartCom 與 WoSign 的故事才剛要開始,前陣子在「Mozilla 在考慮移除 WoSign 的 CA Root」這邊提到的問題,最近 mailing list 上越來愈刺激了。(發現更多沒有通報的問題)

另外也發現 StartCom 被 WoSign (的 CEO) 買下來了,當初因為「Why I stopped using StartSSL (Hint: it involves a Chinese company)」而移除信任,看起來情況只會更糟糕...

Mozilla 在考慮移除 WoSign 的 CA Root

雖然平常早就把 WoSign 移除信任,但在「Mozilla考虑对沃通CA采取行动」這邊看到有趣的消息,翻了一下 Gervase Markham 發表的原文還蠻精彩的:「Incidents involving the CA WoSign」。

第一次事件 (Incident 0) 是在 2015/04/23,攻擊者只要能夠證明他能控制某個 TCP port,就會發出 certificate:

On or around April 23rd, 2015, WoSign's certificate issuance system for their free certificates allowed the applicant to choose any port for validation. Once validation had been completed, WoSign would issue certificates for that domain. A researcher was able to obtain a certificate for a university by opening a high-numbered port (>50,000) and getting WoSign to use that port for validation of control.

設計不良造成的資安事件總是會發生。重點在於 Google 知道,但 Mozilla 完全不知道:(我講得很保守是因為這個句子在 thread 後面被澄清解釋的更慘,參考後文)

This problem was reported to Google, and thence to WoSign and resolved. Mozilla only became aware of it recently.

更嚴重的是,這次的事件在 WoSign 的稽核上沒有出現:

* This misissuance incident did not turn up on WoSign's subsequent BR audit[1].

第二次事件 (Incident 1) 是在 2015 年六月,也是資安設計的問題,當你可以拿到 WoSign 所指定的 subdomain 控制權後,你就可以拿到 parent domain 的 certificate,而這次甚至被拿到 GitHub 全系列的 certificate:

The reporter proved the problem in two ways. They accidentally discovered it when trying to get a certificate for med.ucf.edu and mistakenly also applied for www.ucf.edu, which was approved. They then confirmed the problem by using their control of theiraccount.github.com/theiraccount.github.io to get a cert for github.com, github.io, and www.github.io.

嗯,也沒通報:

* This misissuance incident was not reported to Mozilla by WoSign as it should have been (see above).

嗯,稽核也沒出來:

* This misissuance incident did not turn up on WoSign's subsequent BR audit[1].

嗯,被拿到的 domain (ucf.edu) 也沒 revoke:(可以從「crt.sh | 29647048」這邊看到)

They reported this to WoSign, giving only the Github certificate as an example. That cert was revoked and the vulnerability was fixed. However recently, they got in touch with Google to note that the ucf.edu cert still had not been revoked almost a year later.

第三次事件 (Incident 2) 則是在 2016 年七月,由於現在大多數的瀏覽器都會對 2016 後簽出的 SHA-1 憑證直接標示為不安全,而 WoSign 的 API 提供造假,讓簽名日期 (notBefore) 簽在 2015/12/20:

Using the value "1" led to a certificate which had a notBefore date (usage start date) of 20th December 2015, and which was signed using the SHA-1 checksum algorithm.

嗯,然後否認造假:

* WoSign deny that their code backdated the certificates in order to avoid browser-based restrictions - they say "this date is the day we stop to use this code"[4]. If that is true, it is not clear to us how StartCom came to deploy WoSign code that WoSign itself had abandoned.

嗯,然後還是沒有回報給 Mozilla:

* This misissuance incident was not reported to Mozilla by WoSign as it should have been.

稽核報告應該是因為這太新,還沒開始做?

另外在 thread 討論時,Google 的 Ryan Sleevi 澄清的更慘:

Clarification: In none of these incidents was Google notified proactively by WoSign. Instead, Google received communication from internal or external researchers regarding these issues, either prior to resolution or much later after the fact, and subsequently contacted WoSign regarding them.

It was only when Google found out recently that other programs were NOT notified, proactively, as had been expected, that Google shared the details it was aware of regarding various CA incidents, including those of WoSign, mentioned in this thread.

也就是說,是 Google 主動發現這些問題,並且通報 WoSign。後來過了許久發現 WoSign 沒有照規定通報其他 CA Root 管理單位 (以這邊來說是 Mozilla),於是 Google 決定主動通報其他單位,然後大~爆~炸~

在密碼學理論裡,CA 架構是靠著稽核建立信任的,這次的事情又再次證實這個問題 (但目前沒有其他好的機制可以做)。來猜測下場的話,我的預期是會像拔掉 CNNIC 的作法拔掉信任,但針對之前發出的 certificate 設為白名單 (直到過期):

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