Home News New Microsoft Exchange ‘ProxyToken’ Flaw Lets Attackers Reconfigure Mailboxes

    New Microsoft Exchange ‘ProxyToken’ Flaw Lets Attackers Reconfigure Mailboxes

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    Microsoft Exchange

    Particulars have emerged a few now-patched safety vulnerability impacting Microsoft Trade Server that might be weaponized by an unauthenticated attacker to switch 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 Heart 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 impression, 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 concern resides in a characteristic referred to 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

    Nevertheless, since Trade must be particularly configured to make use of the characteristic and have the back-end perform the checks, it results in a situation by which the module dealing with this delegation (“DelegatedAuthModule”) is not loaded underneath default configuration, culminating in a bypass because the back-end fails to authenticate incoming requests based mostly 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 Data Breaches

    The disclosure provides to a rising checklist of Trade Server vulnerabilities which have come to mild 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 comparable 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 clients transfer shortly to use the safety updates from Microsoft.





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