Colin Mc Hugo

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Colin Mc Hugo
Security Engineer Manager & CEO at Quantum Infinite Solutions Group Ltd.
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New Microsoft Exchange ‘ProxyToken’ Flaw Lets Attackers Reconfigure Mailboxes

August 31, 2021
Microsoft Exchange

Particulars have emerged a couple of now-patched safety vulnerability impacting Microsoft Change Server that could possibly be weaponized by an unauthenticated attacker to change server configurations, thus resulting in the disclosure of Personally Identifiable Data (PII).

The problem, tracked as CVE-2021-33766 (CVSS rating: 7.3) and coined “ProxyToken,” was found by Le Xuan Tuyen, a researcher on the Data Safety Middle of Vietnam Posts and Telecommunications Group (VNPT-ISC), and reported by means of the Zero-Day Initiative (ZDI) program in March 2021.

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“With this vulnerability, an unauthenticated attacker can carry out configuration actions on mailboxes belonging to arbitrary customers,” the ZDI said Monday. “As an illustration of the influence, this can be utilized to repeat all emails addressed to a goal and account and ahead them to an account managed by the attacker.”

Microsoft addressed the problem as a part of its Patch Tuesday updates for July 2021.

The safety subject resides in a characteristic known as Delegated Authentication, which refers to a mechanism whereby the front-end web site — the Outlook internet entry (OWA) consumer — passes authentication requests on to the back-end when it detects the presence of a SecurityToken cookie.

Microsoft Exchange ProxyToken

Nonetheless, since Change must be particularly configured to make use of the characteristic and have the back-end perform the checks, it results in a state of affairs through which the module dealing with this delegation (“DelegatedAuthModule”) is not loaded below default configuration, culminating in a bypass because the back-end fails to authenticate incoming requests primarily based on the SecurityToken cookie.

“The online result’s that requests can sail by means of, with out being subjected to authentication on both the entrance or again finish,” ZDI’s Simon Zuckerbraun defined.

Prevent Ransomware Attacks

The disclosure provides to a rising listing of Change Server vulnerabilities which have come to gentle this yr, together with ProxyLogon, ProxyOracle, and ProxyShell, which have actively exploited by risk actors to take over unpatched servers, deploy malicious internet shells and file-encrypting ransomware corresponding to LockFile.

Troublingly, in-the-wild exploit makes an attempt abusing ProxyToken have already been recorded as early as August 10, according to NCC Group safety researcher Wealthy Warren, making it crucial that prospects transfer shortly to use the safety updates from Microsoft.

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