7.8 CVE-2021-27065

CISA Kev Catalog Path Traversal Used by Malware Used by Ransomware Patch Exploit

Microsoft Exchange Server Remote Code Execution Vulnerability
https://nvd.nist.gov/vuln/detail/CVE-2021-27065

Categories

CWE-22 : Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. "Path traversal" is preferred over "directory traversal," but both terms are attack-focused. Automated techniques can find areas where path traversal weaknesses exist. However, tuning or customization may be required to remove or de-prioritize path-traversal problems that are only exploitable by the product's administrator - or other privileged users - and thus potentially valid behavior or, at worst, a bug instead of a vulnerability. Manual white box techniques may be able to provide sufficient code coverage and reduction of false positives if all file access operations can be assessed within limited time constraints. For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server. Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth. Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations. When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues. Large language model (LLM) management tool does notvalidate the format of a digest value (CWE-1287) from aprivate, untrusted model registry, enabling relativepath traversal (CWE-23), a.k.a. Probllama Chain: API for text generation using Large Language Models (LLMs) doesnot include the "\" Windows folder separator in its denylist (CWE-184)when attempting to prevent Local File Inclusion via path traversal(CWE-22), allowing deletion of arbitrary files on Windows systems. Chain: a learning management tool debugger uses external input to locate previous session logs (CWE-73) and does not properly validate the given path (CWE-20), allowing for filesystem path traversal using "../" sequences (CWE-24) Python package manager does not correctly restrict the filename specified in a Content-Disposition header, allowing arbitrary file read using path traversal sequences such as "../" Python package constructs filenames using an unsafe os.path.join call on untrusted input, allowing absolute path traversal because os.path.join resets the pathname to an absolute path that is specified as part of the input. directory traversal in Go-based Kubernetes operator app allows accessing data from the controller's pod file system via ../ sequences in a yaml file 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. a Kubernetes package manager written in Go allows malicious plugins to inject path traversal sequences into a plugin archive ("Zip slip") to copy a file outside the intended directory Chain: security product has improper input validation (CWE-20) leading to directory traversal (CWE-22), as exploited in the wild per CISA KEV. Go-based archive library allows extraction of files to locations outside of the target folder with "../" path traversal sequences in filenames in a zip file, aka "Zip Slip" Newsletter module allows reading arbitrary files using "../" sequences. Chain: PHP app uses extract for register_globals compatibility layer (CWE-621), enabling path traversal (CWE-22) FTP server allows deletion of arbitrary files using ".." in the DELE command. FTP server allows creation of arbitrary directories using ".." in the MKD command. FTP service for a Bluetooth device allows listing of directories, and creation or reading of files using ".." sequences. Software package maintenance program allows overwriting arbitrary files using "../" sequences. Bulletin board allows attackers to determine the existence of files using the avatar. PHP program allows arbitrary code execution using ".." in filenames that are fed to the include() function. Overwrite of files using a .. in a Torrent file. Chat program allows overwriting files using a custom smiley request. Chain: external control of values for user's desired language and theme enables path traversal. Chain: library file sends a redirect if it is directly requested but continues to execute, allowing remote file inclusion and path traversal.

References

af854a3a-2127-422b-91ae-364da2661108 Patch Exploit

http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Rem... Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Col... Exploit Third Party Advisory VDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-2... Patch Vendor Advisory

secure@microsoft.com Patch Exploit

http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Rem... Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Col... Exploit Third Party Advisory VDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-2... Patch Vendor Advisory

CPE

cpe	start	end
Configuration 1
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21::::::
cpe:2.3:a:microsoft:exchange_server:2013:sp1::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8::::::
cpe:2.3:a:microsoft:exchange_server:2019:-::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8::::::

REMEDIATION

Patch

Url
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-2...
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-2...

EXPLOITS

Exploit-db.com

id	description	date
No known exploits

POC Github

Url
No known exploits

Other Nist (github, ...)

Url
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Rem...
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Col...
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Rem...
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Col...

CAPEC

Common Attack Pattern Enumerations and Classifications

id	description	severity
126	Path Traversal An adversary uses path manipulation methods to exploit insufficient input validation of a target to obtain access to data that should be not be retrievable by ordinary well-formed requests. A typical variety of this attack involves specifying a path to a desired file together with dot-dot-slash characters, resulting in the file access API or function traversing out of the intended directory structure and into the root file system. By replacing or modifying the expected path information the access function or API retrieves the file desired by the attacker. These attacks either involve the attacker providing a complete path to a targeted file or using control characters (e.g. path separators (/ or ) and/or dots (.)) to reach desired directories or files. [Fingerprinting of the operating system] In order to perform a valid path traversal, the attacker needs to know what the underlying OS is so that the proper file seperator is used. [Survey the Application to Identify User-controllable Inputs] The attacker surveys the target application to identify all user-controllable file inputs [Vary inputs, looking for malicious results] Depending on whether the application being exploited is a remote or local one, the attacker crafts the appropriate malicious input containing the path of the targeted file or other file system control syntax to be passed to the application [Manipulate files accessible by the application] The attacker may steal information or directly manipulate files (delete, copy, flush, etc.)	Very High
64	Using Slashes and URL Encoding Combined to Bypass Validation Logic This attack targets the encoding of the URL combined with the encoding of the slash characters. An attacker can take advantage of the multiple ways of encoding a URL and abuse the interpretation of the URL. A URL may contain special character that need special syntax handling in order to be interpreted. Special characters are represented using a percentage character followed by two digits representing the octet code of the original character (%HEX-CODE). For instance US-ASCII space character would be represented with %20. This is often referred as escaped ending or percent-encoding. Since the server decodes the URL from the requests, it may restrict the access to some URL paths by validating and filtering out the URL requests it received. An attacker will try to craft an URL with a sequence of special characters which once interpreted by the server will be equivalent to a forbidden URL. It can be difficult to protect against this attack since the URL can contain other format of encoding such as UTF-8 encoding, Unicode-encoding, etc. The attacker accesses the server using a specific URL. The attacker tries to encode some special characters in the URL. The attacker find out that some characters are not filtered properly. The attacker crafts a malicious URL string request and sends it to the server. The server decodes and interprets the URL string. Unfortunately since the input filtering is not done properly, the special characters have harmful consequences.	High
76	Manipulating Web Input to File System Calls An attacker manipulates inputs to the target software which the target software passes to file system calls in the OS. The goal is to gain access to, and perhaps modify, areas of the file system that the target software did not intend to be accessible. [Fingerprinting of the operating system] In order to create a valid file injection, the attacker needs to know what the underlying OS is so that the proper file seperator is used. [Survey the Application to Identify User-controllable Inputs] The attacker surveys the target application to identify all user-controllable inputs, possibly as a valid and authenticated user [Vary inputs, looking for malicious results] Depending on whether the application being exploited is a remote or local one, the attacker crafts the appropriate malicious input containing the path of the targeted file or other file system control syntax to be passed to the application [Manipulate files accessible by the application] The attacker may steal information or directly manipulate files (delete, copy, flush, etc.)	Very High
78	Using Escaped Slashes in Alternate Encoding This attack targets the use of the backslash in alternate encoding. An adversary can provide a backslash as a leading character and causes a parser to believe that the next character is special. This is called an escape. By using that trick, the adversary tries to exploit alternate ways to encode the same character which leads to filter problems and opens avenues to attack. [Survey the application for user-controllable inputs] Using a browser, an automated tool or by inspecting the application, an adversary records all entry points to the application. [Probe entry points to locate vulnerabilities] The adversary uses the entry points gathered in the "Explore" phase as a target list and attempts to escape multiple different special characters using a backslash. [Manipulate input] Once the adversary determines how to bypass filters that filter out special characters using an escaped slash, they will manipulate the user input in a way that is not intended by the application.	High
79	Using Slashes in Alternate Encoding This attack targets the encoding of the Slash characters. An adversary would try to exploit common filtering problems related to the use of the slashes characters to gain access to resources on the target host. Directory-driven systems, such as file systems and databases, typically use the slash character to indicate traversal between directories or other container components. For murky historical reasons, PCs (and, as a result, Microsoft OSs) choose to use a backslash, whereas the UNIX world typically makes use of the forward slash. The schizophrenic result is that many MS-based systems are required to understand both forms of the slash. This gives the adversary many opportunities to discover and abuse a number of common filtering problems. The goal of this pattern is to discover server software that only applies filters to one version, but not the other. [Survey the application for user-controllable inputs] Using a browser, an automated tool or by inspecting the application, an adversary records all entry points to the application. [Probe entry points to locate vulnerabilities] The adversary uses the entry points gathered in the "Explore" phase as a target list and looks for areas where user input is used to access resources on the target host. The adversary attempts different encodings of slash characters to bypass input filters. [Traverse application directories] Once the adversary determines how to bypass filters that filter out slash characters, they will manipulate the user input to include slashes in order to traverse directories and access resources that are not intended for the user.	High

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cpe	start	end
Configuration 1
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21::::::
cpe:2.3:a:microsoft:exchange_server:2013:sp1::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19::::::
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8::::::
cpe:2.3:a:microsoft:exchange_server:2019:-::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7::::::
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8::::::