CVE-2026-115931 in Postiz
Summary
by MITRE • 10/24/2026
Postiz lets a signed-in user ask the backend to run a function on one of their connected channels. The backend did not restrict which functions can be requested, so a user could call internal helper functions that were never meant to be reachable from the web interface.
One of those helpers reads a file from the server's disk. A user who connects a channel whose stored token is a file path can have the backend return the contents of any file it can read, including its environment, which holds the secret used to sign login sessions, the database address and the credentials of connected services. Another helper makes the backend process exit with a single request. Self-registration is open by default, so no existing account and no action by another user is needed.
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Analysis
by VulDB Data Team • 10/24/2026
The vulnerability in Postiz represents a critical failure in access control logic, specifically classified under CWE-284 Improper Access Control. The core issue stems from the application's backend architecture, which exposes internal helper functions to the web interface without implementing sufficient restrictions on user input or function invocation paths. In a secure design, API endpoints should strictly map to intended public-facing operations, while internal utility functions must remain inaccessible via direct HTTP requests. By allowing any signed-in user to specify arbitrary functions for execution, the application violates the principle of least privilege and fails to enforce proper separation between external interfaces and internal system logic. This architectural flaw enables an attacker to bypass standard authentication boundaries not by breaking encryption or stealing credentials initially, but by exploiting the trust relationship inherent in a valid session token to invoke privileged backend methods that were never intended for public consumption.
The exploitation of this vulnerability leads to severe information disclosure through a server-side file read operation. When a user connects a channel, they provide configuration data including authentication tokens. The application stores these tokens and later processes them using an internal helper function designed to read files from the disk. Because there is no validation on the content of the stored token or the path it represents, an attacker can manipulate this field to contain a file system path rather than a standard API key. Upon subsequent processing by the vulnerable backend component, the application interprets this input as a literal file path and returns its contents directly in the response. This mechanism effectively transforms the vulnerability into a Local File Inclusion or arbitrary file read scenario, allowing the attacker to extract sensitive data stored on the server's filesystem with the privileges of the running application process.
The impact of this information disclosure is profound because it grants access to critical system secrets and credentials. The files accessible through this vector include environment configuration files that contain the secret key used for signing login sessions. Compromise of this session secret allows an attacker to forge valid authentication tokens, effectively achieving full account takeover without needing a password or multi-factor bypass. Furthermore, these exposed configurations often reveal database connection strings, including host addresses and credentials, as well as API keys for third-party services connected by the user. This cascading effect means that compromising one Postiz instance can lead to lateral movement into internal databases and external service accounts, significantly expanding the blast radius of the initial vulnerability beyond just the web application itself.
In addition to data exfiltration, the vulnerability includes a denial-of-service vector through an unauthenticated or authenticated process termination function. A specific helper allows a user request to cause the backend process to exit immediately. While this does not directly compromise confidentiality or integrity in the traditional sense, it disrupts availability for all users of the service. The combination of arbitrary file read and application crash capabilities makes this vulnerability particularly dangerous as it offers multiple avenues for exploitation depending on the attacker's goals, whether that be espionage or disruption.
The risk is further exacerbated by the fact that self-registration is open by default. This configuration means that no pre-existing account or interaction with another user is required to initiate an attack. Any individual can create a new account and immediately begin probing the backend for these exposed functions. From a threat modeling perspective, this aligns with MITRE ATT&CK techniques such as T1078 Valid Accounts, where attackers use legitimate credentials obtained through self-registration or other means to access resources that should be restricted. The lack of input validation on channel tokens serves as a classic example of CWE-20 Improper Input Validation, which directly leads to the insecure direct object reference and file read outcomes observed here.
Mitigation strategies must focus on strict separation of concerns within the backend architecture. Internal helper functions used for system maintenance or data processing should never be exposed via public API endpoints. Instead, these operations should be triggered only by internal application logic after rigorous validation of inputs. Specifically, any user-supplied data that is interpreted as a file path must undergo strict sanitization to ensure it does not traverse outside the intended directory structure and contains no special characters or relative paths like dot-dot-slash sequences. Additionally, implementing an allowlist approach for API endpoints ensures that only explicitly defined functions are callable by users. For immediate remediation, administrators should disable self-registration if possible, enforce strong input validation on all channel configuration fields to prevent file path injection, and rotate the session signing secret immediately to invalidate any potentially forged tokens generated during the window of vulnerability.