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Overview
The Rakuten Viber messaging app for Android V25.7.2.0g and Windows V25.6.0.0-V25.8.1.0, has a flaw in its TLS handshake implementation when using the Cloak proxy configuration. This flaw allows for easy identification of proxy usage, potentially compromising user anonymity.
Description
Rakuten Viber can be configured to use a proxy server. Multiple proxy configurations, including Cloak, are supported. Rakuten Viber in Android V25.7.2.0g and Windows V25.6.0.0–V25.8.1.0 exhibits a flaw in the TLS handshake implementation for Cloak mode. Cloak mode is designed to hide the fact that a proxy or VPN is in use.
However, the Cloak proxy mode has a rigid and easily identified fingerprint, making it trivially identifiable by Deep Packet Inspection (DPI) systems. This allows networks to block Viber traffic, undermining the app’s ability to circumvent censorship and potentially leading to denial of service in certain cases.
Impact
The Cloak-mode proxy traffic fails to hide the use of a proxy. The outgoing data is easily identifiable due to the rigid fingerprint and no longer appears to be normal browser TLS behavior. The user has no indication the proxy is not protecting their data.
Solution
Windows users should upgrade to V27.3.0.0 or later, and Android users should upgrade to V27.2.0.0g or later.
For continued support, Windows users can implement automatic updates for Viber.
Acknowledgements
Thanks to the reporter Oleksii Gaienko, an independent security researcher. This document was written by Laurie Tyzenhaus.

Overview
A command injection vulnerability was identified in the MS-Agent framework that can be triggered through unsanitized prompt-derived input. An attacker can craft untrusted input introduced via a chat prompt or other external content sources, resulting in arbitrary command execution on the target system(s) where the MS-Agent framework is deployed. No patch or vendor statement was obtained during the coordination process.
Description
MS-Agent is a lightweight framework that enables agents to perform autonomous task execution and tool invocation. The MS-Agent framework includes several features, including a Shell tool that enables execution of commands on the target operating system to complete agentic actions.
A vulnerability has been identified that allows unsanitized input to be executed through the Shell tool. This occurs because the software does not sufficiently verify and sanitize content before execution. As a result, an attacker can leverage prompt injection techniques to influence the agent into executing unintended shell commands when interacting with attacker-controlled content.
The Shell tool relies on regular expression–based filtering in the check_safe() method, which is intended to restrict unsafe commands. The implemented default denylist can be bypassed, allowing crafted input to evade validation checks and reach the shell execution layer.
The vulnerability is tracked as:
CVE-2026-2256
Command injection vulnerability in ModelScope’s ms-agent allows an attacker to execute arbitrary operating system commands through crafted prompt-derived input.
This vulnerability may be exploited when the agent is instructed to process or retrieve external content, such as analyzing code, summarizing documents, or performing other tasks that involve interacting with attacker-controlled data. If the retrieved or processed content contains malicious command sequences that bypass the check_safe() validation, the agent may forward those commands to the Shell tool for execution.
The use of a regular expression denylist in the check_safe() method is insufficient to prevent command injection. Denylist-based filtering is inherently fragile and can often be bypassed through encoding, command obfuscation, or alternative shell syntax. In this case, the filtering logic can be circumvented, enabling arbitrary command execution within the execution context of the agent process.
Impact
An attacker who successfully exploits this vulnerability may execute arbitrary operating system commands on the target with the privileges of the MS-Agent process. This may allow modification of system files, lateral movement within the environment, establishment of persistence mechanisms, or exfiltration of sensitive data accessible to the agent.
Solution
No statement was provided by the vendor during coordination efforts. Users should deploy MS-Agent only in environments where ingested content is trusted, validated, or sanitized. Agents with shell execution capabilities should be sandboxed or executed with least-privilege permissions. Additional mitigation strategies include replacing denylist-based filtering with strict allowlists and implementing stronger isolation boundaries for tool execution.
Acknowledgements
Thanks to the reporter, Itamar Yochpaz, for this report. Document written by Christopher Cullen.

Overview
A path traversal vulnerability leading to arbitrary file write exist in PyMuPDF version 1.26.5, within the ‘embedded_get’ function in ‘main.py’. This vulnerability is caused by improper handling of untrusted embedded file metadata, which is used directly as an output path, enabling attackers to write files to arbitrary locations on the local system.
Description
PyMuPDF is a Python interface to the MuPDF document rendering engine, providing capabilities for parsing, rendering, searching, and modifying PDF documents.
The ‘embedded_get’ function in PyMuPDF is responsible for opening the provided PDF along with fetching metadata, such as the file name, if using ‘args.output’ it specifies were the file will be written to on the local system. When ‘args.output’ is not provided, the ‘embedded_get’ function falls back to embedded-file metadata, and opens that value in write-binary mode. Since write-binary mode has no constrictions or safety checks it can write anywhere to the local system.
If the derived output path is not supplied by using ‘args.output’, a crafted PDF can be used to target a location on the local system by using the PDF’s name. When an extracted embedded file using ‘embedded_get’ without specified ‘args.output, the tool can write the extracted content outside the intended directory, potentially to paths on the local system.
Impact
Successful exploitation can result in arbitrary file writing to locations permitted by the executing user. If done under an account with elevated privileges, it may overwrite system files. This can lead to privilege escalation, service disruption, or security bypass. ### Overview
A path traversal vulnerability leading to arbitrary file write exists in PyMuPDF version 1.26.5, within the embedded_get function in __main__.py. This vulnerability is caused by improper handling of untrusted embedded file metadata, which is used directly as an output path, enabling attackers to write files to arbitrary locations on the local system.
Description
PyMuPDF is a Python interface to the MuPDF document rendering engine, providing capabilities for parsing, rendering, searching, and modifying PDF documents.
The embedded_get function in PyMuPDF is responsible for opening the provided PDF along with fetching metadata, such as the file name. If using args.output, it specifies where the file will be written on the local system. When args.output is not provided, the embedded_get function falls back to embedded file metadata and opens that value in write-binary mode. Since write-binary mode has no constrictions nor safety checks, it can write to anywhere on the local system.
If the derived output path is not supplied with args.output, a crafted PDF can be used to target a location on the local system using the name of the PDF. When an embedded file is extracted using embedded_get without specified args.output, the tool can write the extracted content outside the intended directory, potentially to paths on the local system.
Impact
Successful exploitation can result in arbitrary file writing to locations permitted by the executing user. If done under an account with elevated privileges, it may overwrite system files. This can lead to privilege escalation, service disruption, or security bypass.
Solution
PyMuPDF has released version 1.26.7 to address this vulnerability. Affected users are encouraged to update as soon as possible.
Acknowledgements
Thanks to the reporter UKO. This document was written by Michael Bragg.
Solution
PyMuPDF has released version 1.26.7 to address this vulnerability. Affected users are encouraged to update as soon as possible.
Acknowledgements
Thanks to the reporter Jangwoo Choe (UKO). This document was written by Michael Bragg.