Linux 內核被曝存在TCP “SACK PANIC” 遠程拒絕服務漏洞（漏洞編號：CVE-2019-11477,CVE-2019-11478,CVE-2019-11479），攻擊者可利用該漏洞遠程攻擊目標服務器，導致系統崩潰或無法提供服務
漏洞詳情
近日，騰訊雲安全中心情報平台監測到 Netflix 信息安全團隊研究員Jonathan Looney發現 Linux 以及 FreeBSD 等系統內核上存在嚴重遠程DoS漏洞，攻擊者可利用該漏洞構造並發送特定的 SACK 序列請求到目標服務器導致服務器崩潰或拒絕服務。
影響版本
目前已知受影響版本如下：
- FreeBSD 12（使用到 RACK TCP 協議棧）
- CentOS 5（Redhat 官方已停止支持，不再提供補丁）
- CentOS 6
- CentOS 7
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 19.04
- Ubuntu 18.10
安全版本
各大Linux發行廠商已發布內核修復補丁，沒漏洞的內核版本如下：
- CentOS 6 ：2.6.32-754.15.3
- CentOS 7 ：3.10.0-957.21.3
- Ubuntu 18.04 LTS：4.15.0-52.56
- Ubuntu 16.04 LTS：4.4.0-151.178
修復方法
請參照上述【安全版本】升級您的 Linux 服務器內核，參考操作如下：
CentOS
推薦方案：【CentOS 6/7 系列用戶】
yum clean all && yum makecache，進行軟件源更新；yum update kernel -y，更新當前內核版本;reboot，更新后重啟系統生效;uname -a，檢查當前版本是否為上述【安全版本】，如果是，則說明修復成功。
Ubuntu
推薦方案：【Ubuntu 16.04/18.04 LTS 系列用戶】
sudo apt-get update && sudo apt-get install linux-image-generic，進行軟件源更新並安裝最新內核版本；sudo reboot，更新后重啟系統生效；uname -a，檢查當前版本是否為【安全版本】，如果是，則說明修復成功。
Temp
臨時緩解方案：如用戶不方便重啟進行內核補丁更新，可選擇如下方式禁用內核 SACK配置防范漏洞利用（可能會對網絡性能產生一定影響），運行如下命令即可：
echo 'net.ipv4.tcp_sack = 0' >> /etc/sysctl.conf，禁用 SACK 配置；sysctl -p，重載配置，使其生效。
參考
- 官方通告：https://github.com/Netflix/security-bulletins/blob/master/advisories/third-party/2019-001.md
- 社區參考：https://www.openwall.com/lists/oss-security/2019/06/17/5
- 紅帽公告：https://access.redhat.com/security/vulnerabilities/tcpsack
- 騰訊公告：https://cloud.tencent.com/announce/detail/622
附錄
我服務器是CentOS，所以以其為示例：
# 進行軟件源更新
[root@VM_0_3_centos ~]# yum clean all && yum makecache
Loaded plugins: fastestmirror, langpacks
Cleaning repos: epel extras librehat-shadowsocks os updates
Cleaning up list of fastest mirrors
Loaded plugins: fastestmirror, langpacks
Determining fastest mirrors
epel | 5.3 kB 00:00:00
extras | 3.4 kB 00:00:00
librehat-shadowsocks | 3.0 kB 00:00:00
os | 3.6 kB 00:00:00
updates | 3.4 kB 00:00:00
(1/22): epel/7/x86_64/group_gz | 88 kB 00:00:01
(2/22): epel/7/x86_64/updateinfo | 978 kB 00:00:01
(3/22): epel/7/x86_64/prestodelta | 717 B 00:00:00
(4/22): epel/7/x86_64/filelists_db | 11 MB 00:00:06
(5/22): epel/7/x86_64/primary_db | 6.8 MB 00:00:15
(6/22): epel/7/x86_64/updateinfo_zck | 1.4 MB 00:00:00
(6/22): epel/7/x86_64/updateinfo_zck | 1.4 MB 00:00:00
(6/22): epel/7/x86_64/updateinfo_zck | 1.4 MB 00:00:00
(6/22): epel/7/x86_64/updateinfo_zck | 1.4 MB 00:00:00
(6/22): epel/7/x86_64/updateinfo_zck | 1.4 MB 00:00:00
(7/22): extras/7/x86_64/prestodelta | 65 kB 00:00:01
(8/22): extras/7/x86_64/primary_db | 205 kB 00:00:01
(9/22): extras/7/x86_64/other_db | 127 kB 00:00:00
(10/22): librehat-shadowsocks/x86_64/filelists_db | 17 kB 00:00:00
(11/22): librehat-shadowsocks/x86_64/primary_db | 23 kB 00:00:00
(12/22): librehat-shadowsocks/x86_64/other_db | 10 kB 00:00:00
(13/22): os/7/x86_64/group_gz | 166 kB 00:00:00
(14/22): os/7/x86_64/primary_db | 6.0 MB 00:00:03
(15/22): os/7/x86_64/filelists_db | 7.1 MB 00:00:05
(16/22): os/7/x86_64/other_db | 2.6 MB 00:00:00
(17/22): updates/7/x86_64/prestodelta | 797 kB 00:00:00
(18/22): updates/7/x86_64/primary_db | 6.4 MB 00:00:01
(19/22): updates/7/x86_64/other_db | 641 kB 00:00:00
(20/22): updates/7/x86_64/filelists_db | 4.4 MB 00:00:05
epel/7/x86_64/other_db
http://mirrors.tencentyun.com/epel/7/x86_64/repodata/24838144a5b86bb0cd90b22255258aeed11691115ae3c35463e471cbae0f2ab9-other.sqlite.bz2: [Errno 12] Timeout on http://mirrors.tencentyun.com/epel/7/x86_64/repodata/24838144a5b86bb0cd90b22255258aeed11691115ae3c35463e471cbae0f2ab9-other.sqlite.bz2: (28, 'Operation too slow. Less than 1000 bytes/sec transferred the last 30 seconds')
Trying other mirror.
(21/22): extras/7/x86_64/filelists_db | 246 kB 00:00:26
(22/22): epel/7/x86_64/other_db | 3.2 MB 00:00:12
Metadata Cache Created
# 更新內核
[root@VM_0_3_centos ~]# yum update kernel -y
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package kernel.x86_64 0:3.10.0-957.21.3.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
=======================================================================================================================================================================
Package Arch Version Repository Size
=======================================================================================================================================================================
Installing:
kernel x86_64 3.10.0-957.21.3.el7 updates 48 M
Transaction Summary
=======================================================================================================================================================================
Install 1 Package
Total download size: 48 M
Installed size: 63 M
Downloading packages:
Delta RPMs disabled because /usr/bin/applydeltarpm not installed.
kernel-3.10.0-957.21.3.el7.x86_64.rpm | 48 MB 00:00:11
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : kernel-3.10.0-957.21.3.el7.x86_64 1/1
Verifying : kernel-3.10.0-957.21.3.el7.x86_64 1/1
Installed:
kernel.x86_64 0:3.10.0-957.21.3.el7
Complete!
# 重啟
[root@VM_0_3_centos ~]# reboot
# 查看內核版本是否為最新的`3.10.0-957.21.3`
[root@VM_0_3_centos ~]# uname -a
Linux VM_0_3_centos 3.10.0-957.21.3.el7.x86_64 #1 SMP Tue Jun 18 16:35:19 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux