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CVE-2021-42321 is a post-authentication remote code execution vulnerability in Microsoft Exchange Server caused by unsafe deserialization of attacker-controlled data. Analysis of the vulnerable code path indicates the issue involves Exchange deserialization logic in which TypedBinaryFormatter does not correctly propagate a binder into ExchangeBinaryFormatterFactory.CreateBinaryFormatter(), allowing deserialization to proceed with insufficient type restrictions. The vulnerable flow reportedly involves Exchange components handling EWS user configuration data, where serialized content supplied through the BinaryData field of a CreateUserConfiguration request can later be deserialized when the GetClientAccessToken EWS operation is invoked. The deserialization path has been described as passing through Exchange serialization helpers and ultimately reaching a sink involving ClaimsPrincipal, which triggers an additional BinaryFormatter deserialization step without effective filtering. This enables a suitably authenticated attacker to supply a crafted serialized payload and achieve code execution in the Exchange server process.
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2 valid exploits after Mallory filtered fakes, detection scripts, and README-only repos.
This repository contains a single Metasploit module targeting Microsoft Exchange Server vulnerabilities (CVE-2021-42321 and CVE-2022-23277) in the ChainedSerializationBinder component. The exploit requires valid Exchange user credentials and targets Exchange 2016 CU21/CU22 and 2019 CU10/CU11 prior to the March 2022 Security Update. The module leverages authenticated access to the Exchange Web Services (EWS) endpoint (/ews/exchange.asmx) to create a malicious user configuration object, which is then deserialized to achieve remote code execution as SYSTEM. The exploit supports multiple payload types, including direct command execution, file droppers, and PowerShell stagers, and is fully integrated into the Metasploit framework, allowing for payload customization and automated exploitation. The code is mature, weaponized, and suitable for post-authentication exploitation scenarios. The only fingerprintable endpoint is the EWS SOAP endpoint, which is standard for Exchange servers.
This repository contains a proof-of-concept exploit for CVE-2021-42321, a remote code execution vulnerability in Microsoft Exchange Server. The main file, 'CVE-2021-42321_poc.py', is a Python script that crafts and sends a malicious serialized .NET payload (gadgetData) to the Exchange Web Services (EWS) SOAP API endpoint '/ews/exchange.asmx' on a target Exchange server. The script authenticates using NTLM credentials and performs a sequence of SOAP requests to first retrieve the inbox folder ID, delete any existing user configuration, and then create a new user configuration containing the malicious payload. The payload is designed to trigger code execution on the server (e.g., launching calc or mspaint). The exploit requires valid credentials and a vulnerable Exchange Server. The repository also includes a brief README referencing the CVE and the official Microsoft patch. No hardcoded endpoints are present; the user must specify the target Exchange server URL and credentials.
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A Microsoft Exchange vulnerability (CVE-2021-42321) referenced in the context of a threat actor claiming to sell an 'implementation' (i.e., exploit capability) for it to gain access to victim networks.
A vulnerability listed as one of several publicly available exploits leveraged by Forest Blizzard.
A post-auth remote code execution deserialization vulnerability in Microsoft Exchange Server. The content describes technical analysis of the deserialization sink and source, and shows how authenticated attackers can achieve RCE via EWS user configuration data and GetClientAccessToken.
A specific vulnerability in Microsoft Exchange that, per the content, was demonstrated at Tianfu Cup 2021 and then rapidly exploited in the wild shortly thereafter—suggesting fast operationalization by threat actors with early access.
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