Tag: aslr

FreeBSD 14.0 釋出

FreeBSD 14.0-RELEASE 的公告也出來了：「FreeBSD 14.0-RELEASE Announcement」，比較完整的 release notes 在「FreeBSD 14.0-RELEASE Release Notes」。

先從官方列的 highlight 來看，首先比較重要的是 GENERIC kernel 支援 1024 cores：

FreeBSD supports up to 1024 cores on the amd64 and arm64 platforms.

看了一下 commit log 是從 256 變成 1024。

先就 x86-64 這邊來看，目前「家用」最多的應該是 AMD 的 7995WX (96 cores)，舊版的 256 限制應該也還能撐住，但看 commit log 有提到，主要是預期這幾年應該會有更暴力的機器出現。

另外一塊是伺服器端，Intel 這邊有 8 sockets 的版本 (參考「Intel Xeon Sapphire Rapids to Scale to 4 and 8 Sockets」)，如果都是接 8490H 的話就是 480 cores 了。

ARM 的話好像也可以堆，但不熟...

另外一個提到的重點是 TCP 預設的 congestion control 改成 CUBIC：

The default congestion control mechanism for TCP is now CUBIC.

翻 commit log 可以看到是從 NewReno 換成 CUBIC 的，這樣就跟 Linux kernel 預設值一樣了。

再來比較重要的是在 release notes 裡面提到的，FreeBSD 15.0 將會拔光 32-bit 環境的支援，只留 armv7，這代表 Raspberry Pi 第一代的 armv6 也被淘汰掉了：

FreeBSD 15.0 is not expected to include support for 32-bit platforms other than armv7. The armv6, i386, and powerpc platforms are deprecated and will be removed. 64-bit systems will still be able to run older 32-bit binaries.

然後有些我自己翻覺得還蠻有趣的。

首先是看到 non-root 的 chroot：

The chroot facility supports unprivileged operation, and the chroot(8) program has a -n option to enable its use. a40cf4175c90 (Sponsored by EPSRC)

然後把 OpenSSH 內對 FIDO/U2F 的支援開起來了：

The use of FIDO/U2F hardware authenticators has been enabled in ssh, using the new public key types ecdsa-sk and ed25519-sk, along with corresponding certificate types. FIDO/U2F support is described in https://www.openssh.com/txt/release-8.2. e9a994639b2a (Sponsored by The FreeBSD Foundation)

ASLR 預設開啟：

Address Space Layout Randomization (ASLR) is enabled for 64-bit executables by default. It can be disabled as needed if applications fail unexpectedly, for example with segmentation faults. To disable for a single invocation, use the proccontrol(1) command: proccontrol -m aslr -s disable command. To disable ASLR for all invocations of a binary, use the elfctl(1) command: elfctl -e +noaslr file. Problems should be reported via the problem reporting system, https://bugs.freebsd.org, or posting to the freebsd-stable@FreeBSD.org mailing list. b014e0f15bc7 (Sponsored by Stormshield)

然後先前被罵臭頭的 WireGuard 支援也放回來了：(「FreeBSD & pfSense 上的 WireGuard 問題」)

The kernel wg(4) WireGuard driver has been reintegrated; it provides Virtual Private Network (VPN) interfaces using the WireGuard protocol. 744bfb213144 (Sponsored by Rubicon Communications, LLC ("Netgate") and The FreeBSD Foundation)

然後看到 Netflix 贊助的 kTLS 支援 TLS 1.3：

KTLS (the kernel TLS implementation) has added receive offload support for TLS 1.3. Receive offload is now supported for TLS 1.1 through 1.3; send offload is supported for TLS 1.0 through 1.3. 05a1d0f5d7ac (Sponsored by Netflix)

然後 FreeBSD 長久以來 root 預設用的 /bin/csh 改成 /bin/sh 了：

The default shell for the root user is now sh(1), which has many new features for interactive use. d410b585b6f0

預設的 MTA 變成 dma (Dragonfly Mail Agent)，看名字加上翻了一下 manpage，確認是從 Dragonfly BSD 移植過來的：

The default mail transport agent (MTA) is now the Dragonfly Mail Agent (dma(8)) rather than sendmail(8). Configuration of the MTA is done via mailer.conf(5). sendmail(8) and its configuration remain available. a67b925ff3e5

然後 portsnap 被拔掉了，現在就建議直接用 git 拉了，算是功成身退了：

The portsnap(8) utility has been removed. Users are encouraged to fetch the ports tree by using pkg install git and then git clone https://git.FreeBSD.org/ports.git /usr/ports. df53ae0fdd98

而 mergemaster 也被換成 etcupdate 了：

mergemaster(8) has been deprecated. Its replacement is etcupdate(8). 398b12691b4f (Sponsored by The FreeBSD Foundation)

然後支援 tarfs，而且可以用 zstd：

The tarfs(5) file system has been added, which is backed by POSIX tar archives optionally compressed with zstd(1). 69d94f4c7608 (Sponsored by Juniper Networks, Inc.) (Sponsored by Klara, Inc.)

好久沒看 FreeBSD 的 release notes...

7-Zip 的 RCE 安全性問題

7-Zip 被發現安全性問題 (CVE-2018-10115)：「7-Zip: From Uninitialized Memory to Remote Code Execution」。而在 2018/04/30 推出的 18.05 修正了這個問題：「7-Zip 18.05」。

The vulnerability in RAR unpacking code was fixed (CVE-2018-10115).

除了修正以外，另外也開了 ASLR，對安全性會多一些防禦：

2018-03-06 - Discovery
2018-03-06 - Report
2018-04-14 - MITRE assigned CVE-2018-10115
2018-04-30 - 7-Zip 18.05 released, fixing CVE-2018-10115 and enabling ASLR on the executables.

手上有裝 7-Zip 的人要記得更新...

CVE-2015-7547：getaddrinfo() 的 RCE (Remote Code Execution) 慘案

Google 寫了一篇關於 CVE-2015-7547 的安全性問題：「CVE-2015-7547: glibc getaddrinfo stack-based buffer overflow」。

Google 的工程師在找 OpenSSH 連到某台特定主機就會 segfault 的通靈過程中，發現問題不在 OpenSSH，而是在更底層的 glibc 導致 segfault：

Recently a Google engineer noticed that their SSH client segfaulted every time they tried to connect to a specific host. That engineer filed a ticket to investigate the behavior and after an intense investigation we discovered the issue lay in glibc and not in SSH as we were expecting.

由於等級到了 glibc 這種每台 Linux 都有裝的情況，在不經意的情況下發生 segfault，表示在刻意攻擊的情況下可能會很糟糕，所以 Google 投入了人力研究，想知道這個漏洞到底可以做到什麼程度：

Thanks to this engineer’s keen observation, we were able determine that the issue could result in remote code execution. We immediately began an in-depth analysis of the issue to determine whether it could be exploited, and possible fixes. We saw this as a challenge, and after some intense hacking sessions, we were able to craft a full working exploit!

在研究過程中 Google 發現 Red Hat 的人也在研究同樣的問題：「(CVE-2015-7547) - In send_dg, the recvfrom function is NOT always using the buffer size of a newly created buffer (CVE-2015-7547)」：

In the course of our investigation, and to our surprise, we learned that the glibc maintainers had previously been alerted of the issue via their bug tracker in July, 2015. (bug). We couldn't immediately tell whether the bug fix was underway, so we worked hard to make sure we understood the issue and then reached out to the glibc maintainers. To our delight, Florian Weimer and Carlos O’Donell of Red Hat had also been studying the bug’s impact, albeit completely independently! Due to the sensitive nature of the issue, the investigation, patch creation, and regression tests performed primarily by Florian and Carlos had continued “off-bug.”

攻擊本身需要繞過反制機制 (像是 ASLR)，但仍然是可行的，Google 的人已經成功寫出 exploit code：

Remote code execution is possible, but not straightforward. It requires bypassing the security mitigations present on the system, such as ASLR. We will not release our exploit code, but a non-weaponized Proof of Concept has been made available simultaneously with this blog post.

技術細節在 Google 的文章裡也有提到，buffer 大小固定為 2048 bytes，但取得時有可能超過 2048 bytes，於是造成 buffer overflow：

glibc reserves 2048 bytes in the stack through alloca() for the DNS answer at _nss_dns_gethostbyname4_r() for hosting responses to a DNS query.

Later on, at send_dg() and send_vc(), if the response is larger than 2048 bytes, a new buffer is allocated from the heap and all the information (buffer pointer, new buffer size and response size) is updated.

另外 glibc 官方的 mailing list 上也有說明：「[PATCH] CVE-2015-7547 --- glibc getaddrinfo() stack-based buffer overflow」。