9 CVE-2021-34523

CISA Kev Catalog Used by Malware Used by Ransomware Patch Exploit

Microsoft Exchange Server Elevation of Privilege Vulnerability
https://nvd.nist.gov/vuln/detail/CVE-2021-34523

Categories

CWE-287 : Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. An alternate term is "authentification", which appears to be most commonly used by people from non-English-speaking countries. "AuthN" is typically used as an abbreviation of "authentication" within the web application security community. It is also distinct from "AuthZ," which is an abbreviation of "authorization." The use of "Auth" as an abbreviation is discouraged, since it could be used for either authentication or authorization. "AuthC" is used as an abbreviation of "authentication," but it appears to used less frequently than "AuthN." Use an authentication framework or library such as the OWASP ESAPI Authentication feature. Chat application skips validation when Central Authentication Service(CAS) is enabled, effectively removing the second factor fromtwo-factor authentication Python-based authentication proxy does not enforce password authentication during the initial handshake, allowing the client to bypass authentication by specifying a 'None' authentication type. Chain: Web UI for a Python RPC framework does not use regex anchors to validate user login emails (CWE-777), potentially allowing bypass of OAuth (CWE-1390). TCP-based protocol in Programmable Logic Controller (PLC) has no authentication. Condition Monitor uses a protocol that does not require authentication. Safety Instrumented System uses proprietary TCP protocols with no authentication. Distributed Control System (DCS) uses a protocol that has no authentication. SCADA system only uses client-side authentication, allowing adversaries to impersonate other users. Chain: Python-based HTTP Proxy server uses the wrong boolean operators (CWE-480) causing an incorrect comparison (CWE-697) that identifies an authN failure if all three conditions are met instead of only one, allowing bypass of the proxy authentication (CWE-1390) Chain: Cloud computing virtualization platform does not require authentication for upload of a tar format file (CWE-306), then uses .. path traversal sequences (CWE-23) in the file to access unexpected files, as exploited in the wild per CISA KEV. IT management product does not perform authentication for some REST API requests, as exploited in the wild per CISA KEV. Firmware for a WiFi router uses a hard-coded password for a BusyBox shell, allowing bypass of authentication through the UART port Bluetooth speaker does not require authentication for the debug functionality on the UART port, allowing root shell access Default setting in workflow management product allows all API requests without authentication, as exploited in the wild per CISA KEV. Stack-based buffer overflows in SFK for wifi chipset used for IoT/embedded devices, as exploited in the wild per CISA KEV. Mail server does not properly check an access token before executing a Powershell command, as exploited in the wild per CISA KEV. Chain: user is not prompted for a second authentication factor (CWE-287) when changing the case of their username (CWE-178), as exploited in the wild per CISA KEV. Authentication bypass by appending specific parameters and values to a URI, as exploited in the wild per CISA KEV. Mail server does not generate a unique key during installation, as exploited in the wild per CISA KEV. LDAP Go package allows authentication bypass using an empty password, causing an unauthenticated LDAP bind login script for guestbook allows bypassing authentication by setting a "login_ok" parameter to 1. admin script allows authentication bypass by setting a cookie value to "LOGGEDIN". VOIP product allows authentication bypass using 127.0.0.1 in the Host header. product uses default "Allow" action, instead of default deny, leading to authentication bypass. chain: redirect without exit (CWE-698) leads to resultant authentication bypass. product does not restrict access to a listening port for a critical service, allowing authentication to be bypassed. product does not properly implement a security-related configuration setting, allowing authentication bypass. authentication routine returns "nil" instead of "false" in some situations, allowing authentication bypass using an invalid username. authentication update script does not properly handle when admin does not select any authentication modules, allowing authentication bypass. use of LDAP authentication with anonymous binds causes empty password to result in successful authentication product authentication succeeds if user-provided MD5 hash matches the hash in its database; this can be subjected to replay attacks. chain: product generates predictable MD5 hashes using a constant value combined with username, allowing authentication bypass.

References

secure@microsoft.com Patch Exploit

http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Rem... Exploit Third Party Advisory VDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-3... Patch Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-822/ Third Party Advisory VDB Entry

CPE

cpe	start	end
Configuration 1
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9::::::

REMEDIATION

Patch

Url
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-3...

EXPLOITS

Exploit-db.com

id	description	date
No known exploits

POC Github

Url
https://github.com/mithridates1313/ProxyShell_POC

Other Nist (github, ...)

Url
http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Rem...

CAPEC

Common Attack Pattern Enumerations and Classifications

id	description	severity
114	Authentication Abuse An attacker obtains unauthorized access to an application, service or device either through knowledge of the inherent weaknesses of an authentication mechanism, or by exploiting a flaw in the authentication scheme's implementation. In such an attack an authentication mechanism is functioning but a carefully controlled sequence of events causes the mechanism to grant access to the attacker.	Medium
115	Authentication Bypass An attacker gains access to application, service, or device with the privileges of an authorized or privileged user by evading or circumventing an authentication mechanism. The attacker is therefore able to access protected data without authentication ever having taken place.	Medium
151	Identity Spoofing Identity Spoofing refers to the action of assuming (i.e., taking on) the identity of some other entity (human or non-human) and then using that identity to accomplish a goal. An adversary may craft messages that appear to come from a different principle or use stolen / spoofed authentication credentials.	Medium
194	Fake the Source of Data An adversary takes advantage of improper authentication to provide data or services under a falsified identity. The purpose of using the falsified identity may be to prevent traceability of the provided data or to assume the rights granted to another individual. One of the simplest forms of this attack would be the creation of an email message with a modified "From" field in order to appear that the message was sent from someone other than the actual sender. The root of the attack (in this case the email system) fails to properly authenticate the source and this results in the reader incorrectly performing the instructed action. Results of the attack vary depending on the details of the attack, but common results include privilege escalation, obfuscation of other attacks, and data corruption/manipulation.	Medium
22	Exploiting Trust in Client An attack of this type exploits vulnerabilities in client/server communication channel authentication and data integrity. It leverages the implicit trust a server places in the client, or more importantly, that which the server believes is the client. An attacker executes this type of attack by communicating directly with the server where the server believes it is communicating only with a valid client. There are numerous variations of this type of attack.	High
57	Utilizing REST's Trust in the System Resource to Obtain Sensitive Data This attack utilizes a REST(REpresentational State Transfer)-style applications' trust in the system resources and environment to obtain sensitive data once SSL is terminated. [Find a REST-style application that uses SSL] The adversary must first find a REST-style application that uses SSL to target. Because this attack is easier to carry out from inside of a server network, it is likely that an adversary could have inside knowledge of how services operate. [Insert a listener to sniff client-server communication] The adversary inserts a listener that must exist beyond the point where SSL is terminated. This can be placed on the client side if it is believed that sensitive information is being sent to the client as a response, although most often the listener will be placed on the server side to listen for client authentication information. [Gather information passed in the clear] If developers have not hashed or encrypted data sent in the sniffed request, the adversary will be able to read this data in the clear. Most commonly, they will now have a username or password that they can use to submit requests to the web service just as an authorized user	Very High
593	Session Hijacking This type of attack involves an adversary that exploits weaknesses in an application's use of sessions in performing authentication. The adversary is able to steal or manipulate an active session and use it to gain unathorized access to the application. [Discover Existing Session Token] Through varrying means, an adversary will discover and store an existing session token for some other authenticated user session. [Insert Found Session Token] The attacker attempts to insert a found session token into communication with the targeted application to confirm viability for exploitation. [Session Token Exploitation] The attacker leverages the captured session token to interact with the targeted application in a malicious fashion, impersonating the victim.	Very High
633	Token Impersonation An adversary exploits a weakness in authentication to create an access token (or equivalent) that impersonates a different entity, and then associates a process/thread to that that impersonated token. This action causes a downstream user to make a decision or take action that is based on the assumed identity, and not the response that blocks the adversary.	Medium
650	Upload a Web Shell to a Web Server By exploiting insufficient permissions, it is possible to upload a web shell to a web server in such a way that it can be executed remotely. This shell can have various capabilities, thereby acting as a "gateway" to the underlying web server. The shell might execute at the higher permission level of the web server, providing the ability the execute malicious code at elevated levels.	High
94	Adversary in the Middle (AiTM) [Determine Communication Mechanism] The adversary determines the nature and mechanism of communication between two components, looking for opportunities to exploit. [Position In Between Targets] The adversary inserts themself into the communication channel initially acting as a routing proxy between the two targeted components. [Use Intercepted Data Maliciously] The adversary observes, filters, or alters passed data of its choosing to gain access to sensitive information or to manipulate the actions of the two target components for their own purposes.	Very High

MITRE

Techniques

id	description
T1040	Network Sniffing
T1134	Access Token Manipulation
T1185	Browser Session Hijacking
T1505.003	Server Software Component:Web Shell
T1548	Abuse Elevation Control Mechanism
T1550.001	Use Alternate Authentication Material:Application Access Token
T1557	Adversary-in-the-Middle
T1563	Remote Service Session Hijacking
© 2022 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation.

Mitigations

id	description
T1040	In cloud environments, ensure that users are not granted permissions to create or modify traffic mirrors unless this is explicitly required.
T1134	An adversary must already have administrator level access on the local system to make full use of this technique; be sure to restrict users and accounts to the least privileges they require.
T1185	Close all browser sessions regularly and when they are no longer needed.
T1505.003	Enforce the principle of least privilege by limiting privileges of user accounts so only authorized accounts can modify the web directory.
T1548	Limit the privileges of cloud accounts to assume, create, or impersonate additional roles, policies, and permissions to only those required. Where just-in-time access is enabled, consider requiring manual approval for temporary elevation of privileges.
T1550.001	Update corporate policies to restrict what types of third-party applications may be added to any online service or tool that is linked to the company's information, accounts or network (e.g., Google, Microsoft, Dropbox, Basecamp, GitHub). However, rather than providing high-level guidance on this, be extremely specific—include a list of per-approved applications and deny all others not on the list. Administrators may also block end-user consent through administrative portals, such as the Azure Portal, disabling users from authorizing third-party apps through OAuth and forcing administrative consent.
T1557	Train users to be suspicious about certificate errors. Adversaries may use their own certificates in an attempt to intercept HTTPS traffic. Certificate errors may arise when the application’s certificate does not match the one expected by the host.
T1563	Limit remote user permissions if remote access is necessary.
© 2022 The MITRE Corporation. Esta obra se reproduce y distribuye con el permiso de The MITRE Corporation.

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cpe	start	end
Configuration 1
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9::::::