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Sep 14, 2021
Update 2: Microsoft Zero-Day Vulnerability Announced - CVE-2021-40444
THE THREAT UPDATE 2: As of September 14th, Microsoft has released security patches to address CVE-2021-40444 for all impacted versions of Windows. eSentire has tested the update and confirmed its validity against public exploits. Organizations are strongly recommended to apply these security patches as soon as possible, as exploitation in the wild is ongoing. UPDATE: As of September 11th,…
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eSentire is The Authority in Managed Detection and Response Services, protecting the critical data and applications of 1000+ organizations in 70+ countries from known and unknown cyber threats. Founded in 2001, the company’s mission is to hunt, investigate and stop cyber threats before they become business disrupting events.
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eSentire named a Leader in IDC MarketScape for U.S. Managed Detection and Response Services
August 26, 2021 – Waterloo, ON -  eSentire, recognized globally as the Authority in Managed Detection and Response (MDR), announced today that it has been named a Leader in the IDC MarketScape: U.S. Managed Detection and Response Services 2021 Vendor Assessment (doc #US48129921, August 2021). IDC defines the core services an MDR must provide as follows: reduced time for onboarding, 24/7…
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Security advisories — May 17, 2021

CVE-2021-31166 PoC Released

THE THREAT

On May 16th, 2021, a security researcher released Proof-of-Concept (PoC) exploit code for the Windows IIS server vulnerability CVE-2021-31166 (CVSS: 9.8). With this release, eSentire assesses widespread exploitation of this vulnerability is imminent.

CVE-2021-31166 was publicly announced on May 11th, 2021. Exploitation may allow for either Denial of Service (DoS) or Remote Code Execution (RCE). The currently available PoC exploit code demonstrates a DoS attack. Organizations are strongly recommended to apply security patches for this vulnerability as exploitation is expected.

What we’re doing about it

What you should do about it

Additional information

CVE-2021-31166 is especially concerning as it is considered to be a wormable vulnerability. Wormable vulnerabilities can be abused to allow for automatic spread between vulnerable systems.

In an attack scenario, a threat actor could exploit this vulnerability by sending a specially crafted packet to a targeted server utilizing the HTTP Protocol Stack (http.sys) to process packets. Exploitation is considered simple, increasing the likelihood of exploitation in the immediate future.

eSentire produced an advisory on May 11th, with information on CVE-2021-31166 and other high severity vulnerabilities from Microsoft’s May Patch Tuesday release.

Impacted products:

References:

[1] https://github.com/0vercl0k/CVE-2021-31166
[2] https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-31166
[3] https://www.esentire.com/security-advisories/microsoft-patches-critical-vulnerabilities