Microsoft Security Response Center

**According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability?** Successful exploitation of this vulnerability requires an attacker to win a race condition.

**Is the Preview Pane an attack vector for this vulnerability?** No, the Preview Pane is not an attack vector.

**What privileges could an attacker gain?** An attacker who successfully exploited this vulnerability could gain SYSTEM privileges.

**What type of information could be disclosed by this vulnerability?** An attacker that successfully exploited this vulnerability could recover plaintext from TLS-protected data.

**Are there any more actions I need to take to be protected from this vulnerability?** Yes. Customers vulnerable to this issue would need to enable Extended Protection in order to prevent this attack. For more information, see Exchange Server Support for Windows Extended Protection **Is there more information available about this release of Exchange Server?** For more information on this issue, please see The Exchange Blog.

**Are there any more actions I need to take to be protected from this vulnerability?** Yes. Customers vulnerable to this issue would need to enable Extended Protection in order to prevent this attack. For more information, see Exchange Server Support for Windows Extended Protection **Is there more information available about this release of Exchange Server?** For more information on this issue, please see The Exchange Blog.

**According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability?** Successful exploitation of this vulnerability requires an attacker to win a race condition.

**According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability?** Successful exploitation of this vulnerability requires an attacker to successfully execute a blind XXE attack.

**What privileges could an attacker gain?** An attacker who successfully exploited this vulnerability could gain SYSTEM privileges.

**How could an attacker exploit this vulnerability?** In most situations, an unauthenticated attacker could send a specially crafted packet to a targeted server utilizing the Server Name Indication (SNI) over HTTP Protocol Stack (http.sys) to process packets, causing a denial of service (DOS).