Facebook Google Plus Twitter LinkedIn YouTube RSS Menu Search Resource - BlogResource - WebinarResource - ReportResource - Eventicons_066 icons_067icons_068icons_069icons_070

CVE-2020-0688: Microsoft Exchange Server Static Key Flaw Could Lead to Remote Code Execution

Attackers are probing for vulnerable Microsoft Exchange Servers, as details surrounding a severe flaw were recently made public.

Update 02/27/2020: The proof-of-concept section has been updated to reflect the availability of several exploit scripts, including those that can be used to automate exploitation.

Background

On February 11, Microsoft released a patch for a severe vulnerability in Microsoft Exchange Server as part of its monthly Patch Tuesday updates. Initially, Microsoft labeled this a memory corruption vulnerability in Microsoft Exchange. However, Microsoft has since updated the title and description for the flaw.

Analysis

CVE-2020-0688 is a static key vulnerability in Microsoft Exchange Control Panel (ECP), a component of Microsoft Exchange Server. The use of static keys could allow an authenticated attacker with any privilege level to send a specially crafted request to a vulnerable ECP and gain SYSTEM level arbitrary code execution.

Microsoft rates this flaw as important, but notes that exploitation is more likely, according to its exploitability index.

Vulnerability details

According to researchers at the Zero Day Initiative (ZDI), Microsoft Exchange Server installations “have the same validationKey and decryptionKey” in the MachineKeySection of the web configuration (web.config). As the ZDI notes, these keys are used to secure server-side data stored in serialized form in the ViewState, which is included as part of the requests from the client in the “__VIEWSTATE” parameter. (If this sounds familiar, it’s because we recently blogged about an improper input validation vulnerability in Microsoft SQL Server Reporting Services that also involved serializing untrusted data through the VIEWSTATE parameter.)

To generate a malicious request, the attacker would need to obtain the following parameter values:

Parameter Location
validationKey System.Web.Configuration
validation System.Web.Configuration
VIEWSTATEGENERATOR Exchange Control Panel Source
ASP.NET_SessionId Cookie Field in Request Header

While the first two parameters are static and easily obtainable, the last two parameters require an attacker to log in to the vulnerable ECP instance with valid user credentials. Only then could the attacker capture these parameters from the HTML source and the cookie field in the request header.

Once an attacker has obtained these values, they can generate a serialized payload using ysoserial.net as part of their malicious request to a vulnerable ECP instance.

In their blog, the ZDI shared a YouTube video demonstrating exploitation of this flaw.

Valid user credential requirement

As part of a Twitter thread about the vulnerability, security researcher Kevin Beaumont noted that authentication is “not a big hurdle.” He also noted the availability of tools that can capture employee information from LinkedIn pages and use them to target Outlook Web Access (OWA) “with authentication attempts via credential stuffing.” Beaumont said the tools are “used in active attacks, to gain OWA and ECP access.”

Organizations behind in patching

Microsoft provides a way to identify Exchange Server build numbers through the login pages of OWA and ECP, enabling attackers to identify which servers are potentially vulnerable to CVE-2020-0688.

Beaumont found through “a quick sample” that organizations were “averaging in the years rather than months behind” in patching their Exchange Server instances, which is a major concern.

Attackers probing for vulnerable Microsoft Exchange Servers

Soon after the ZDI’s blog post was published, attackers began probing for vulnerable Microsoft Exchange Servers.

Troy Mursch, chief research officer at Bad Packets, tweeted that “mass scanning activity has begun” for this vulnerability.

Beaumont himself also identified mass scanning activity for the vulnerability based on data from BinaryEdge.

Proof of concept

Details to craft a proof-of-concept for this vulnerability can be found in the ZDI’s blog post. Additionally, several exploit scripts were recently shared on GitHub [1, 2, 3] that can automate exploitation so long as the user has valid credentials.

解决方案

Microsoft released patches for this vulnerability during Patch Tuesday on February 11, 2020, for Microsoft Exchange Server 2010, 2013, 2016 and 2019. Though unconfirmed, this may also affect Microsoft Exchange Server 2007, which reached end of life in April 2017.

Microsoft Exchange Server Version Support Article
2010 Service Pack 3 4536989
2013 Cumulative Update 23 4536988
2016 Cumulative Update 14 4536987
2016 Cumulative Update 15 4536987
2019 Cumulative Update 3 4536987
2019 Cumulative Update 4 4536987

Identifying affected systems

A list of Tenable plugins to identify this vulnerability can be found here.

Get more information

Join Tenable's Security Response Team on the Tenable Community.

Learn more about Tenable, the first Cyber Exposure platform for holistic management of your modern attack surface.

Get a free 30-day trial of Tenable.io Vulnerability Management.

订阅 Tenable 博客

订阅
免费试用 立即购买

选择 Tenable.io

免费试用 30 天

可全面访问基于云的现代化漏洞管理平台,从而以无可比拟的精确度发现并追踪所有资产。 立即注册。

立即购买 Tenable.io

可全面访问基于云的现代化漏洞管理平台,从而以无可比拟的精确度发现并追踪所有资产。 立即购买年度订阅。

65资产

$2,275

立即购买

免费试用 立即购买

免费试用 Nessus Professional

免费试用 7 天

Nessus® 是当今市场上功能最全面的漏洞扫描器。Nessus Professional 可帮助自动化漏洞扫描流程、节省合规周期的时间,并让您调动起 IT 团队的积极性。

购买 Nessus Professional

Nessus® 是当今市场上功能最全面的漏洞扫描器。Nessus Professional 可帮助自动化漏洞扫描流程、节省合规周期的时间,并让您调动起 IT 团队的积极性。

购买多年期许可,即享优惠价格添加高级版支持功能,获取一年 365 天、一天 24 小时的电话、邮件、社区和聊天支持。完整介绍请见此处。

免费试用 立即购买

试用 Tenable.io Web Application Scanning

免费试用 30 天

完整享有专为现代化应用程序而设、属于 Tenable.io 平台组成部分的最新 Web 应用程序扫描功能。可安全扫描全部在线资产组合的漏洞,具有高度准确性,而且无需繁重的手动操作或中断关键的 Web 应用程序。 立即注册。

购买 Tenable.io Web Application Scanning

可全面访问基于云的现代化漏洞管理平台,从而以无可比拟的精确度发现并追踪所有资产。 立即购买年度订阅。

5 FQDN

$3,578

立即购买

免费试用 联系销售人员

试用 Tenable.io Container Security

免费试用 30 天

完整获得已集成至漏洞管理平台之唯一容器安全产品的功能。监控容器映像中的漏洞、恶意软件和策略违规。与持续集成和持续部署 (CI/CD) 系统进行整合,以支持 DevOps 实践、增强安全性并支持企业政策合规。

购买 Tenable.io Container Security

Tenable.io Container Security 经由与构建流程的集成,可供全面了解容器映像的安全性,包括漏洞、恶意软件和策略违规,借以无缝且安全地启用 DevOps 流程。

了解有关 Industrial Security 的详情

获取 Tenable.sc 演示

请将您的联系方式填写在下方表格中,我们的销售代表很快与您联系安排演示。您也可以写下简短评论(不得超过 255 个字符)。请注意,带星号 (*) 的字段为必填项。

免费试用 联系销售人员

试用 Tenable Lumin

免费试用 30 天

通过 Tenable Lumin 直观呈现及探索 Cyber Exposure,长期追踪风险降低状况,并比照同行业者进行基准度量。

购买 Tenable Lumin

联系销售代表,了解 Lumin 如何帮助获取整个企业的洞见并管理网络风险。

申请演示 Tenable.ot

获得符合需求的运营技术安全性。
降低避之不及的风险。