CVE-2026-86157 in Telerik Fiddler Everywhere
Summary
by MITRE • 09/29/2026
Exposure of privileged IPC functionality in Progress Telerik Fiddler Everywhere before version 8.2.0 allows a local, low-privileged attacker who can modify application launch parameters and persuade a user to start the application to replace the application UI or settings with attacker-controlled content. Successful exploitation could result in disclosure of OAuth authentication tokens, execution of locally accessible programs, or unauthorized modification of application-generated configuration files.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified in Progress Telerik Fiddler Everywhere prior to version 8.2.0 represents a critical flaw in the handling of Inter-Process Communication (IPC) mechanisms and local privilege boundaries within the desktop application architecture. This issue stems from an improper exposure of privileged IPC functionality, which allows for unintended interactions between different security contexts on the host system. Specifically, the vulnerability arises because the application does not sufficiently validate or restrict access to certain internal communication channels that are intended for use by elevated processes or trusted components. By exposing these endpoints without adequate authentication or authorization checks, the software creates a pathway through which lower-privileged entities can inject commands or data into higher-privileged contexts. This architectural weakness is particularly dangerous in desktop environments where applications often run with varying levels of system access depending on their configuration and user privileges.
The exploitation vector for this vulnerability requires local access to the target machine and involves social engineering combined with technical manipulation. An attacker who possesses low-level privileges must first modify the application launch parameters, such as command-line arguments or environment variables, before persuading a victim to start Fiddler Everywhere under these altered conditions. This step is crucial because it sets up the specific execution context that triggers the IPC flaw. Once the application launches with the manipulated parameters, the attacker can leverage the exposed privileged functionality to interact with the running process in ways that were not intended by the developers. The core of the attack lies in convincing or forcing the user-initiated session to accept inputs from an untrusted source, effectively bypassing standard security controls through the abuse of legitimate application features.
The operational impact of successfully exploiting this vulnerability is severe and multifaceted, affecting both confidentiality and integrity within the local environment. One primary consequence is the potential disclosure of OAuth authentication tokens stored or processed by Fiddler Everywhere. Since these tools are often used for debugging network traffic involving sensitive web applications, they frequently handle credentials and session tokens in memory or on disk. An attacker gaining access to these tokens can impersonate the user across various online services, leading to unauthorized account access and data breaches beyond the scope of the local machine. Additionally, the vulnerability allows for the execution of locally accessible programs with elevated privileges if the IPC channel permits command injection into a higher-privileged context. This effectively escalates the attacker's rights from low-level user permissions to those of the application or even system level, depending on how Fiddler is configured and launched.
Furthermore, the flaw enables unauthorized modification of application-generated configuration files. These files often contain sensitive settings, proxy configurations, and cached data that are critical for the proper functioning of the tool and potentially other integrated systems. By altering these files, an attacker can persist their presence within the environment or redirect network traffic to malicious servers without detection. This capability undermines the integrity of the development and debugging workflow, as any subsequent sessions may operate under compromised settings. The combination of credential theft, arbitrary code execution potential, and configuration tampering creates a high-risk scenario that compromises not only the individual user but potentially entire organizational networks if such tools are used in enterprise environments with shared credentials or sensitive internal traffic monitoring.
From a standards perspective, this vulnerability aligns closely with CWE-250, which describes Execution with Unnecessary Privileges, and CWE-749, which relates to Exposure of Dangerous Method for Attackers. The attack technique also maps to MITRE ATT&CK tactics involving Initial Access through social engineering and Persistence or Privilege Escalation via local process manipulation. To mitigate this risk, users must upgrade immediately to version 8.2.0 or later, where the IPC exposure has been addressed by implementing stricter access controls and input validation on privileged endpoints. Administrators should also enforce least-privilege principles when deploying such tools in corporate environments, ensuring that applications do not run with unnecessary elevated rights unless absolutely required for specific debugging tasks. Regular auditing of application launch configurations and monitoring for unusual process behavior can further reduce the attack surface associated with this class of vulnerabilities.