JSON Injection in Bitwarden Server

Executive Summary

This vulnerability is a JSON injection issue in Bitwarden Server versions before 2026.5.0. It occurs in the IntegrationTemplateProcessor.ReplaceTokens() function, which substitutes user-controlled values into event-integration templates without properly encoding them as JSON.

When an organization configures an event integration template that references user-controlled tokens such as #ActingUserName# or #UserName# (which come from a member's display name), an authenticated user can exploit this by setting their display name to include JSON metacharacters. This allows them to inject arbitrary key-value pairs into the JSON payloads sent to webhook, SIEM, Slack, Teams, or Datadog endpoints.

Injected fields become indistinguishable from legitimate template output, potentially manipulating the data received by these integrations.

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Impact Analysis

This vulnerability allows an authenticated member to inject arbitrary JSON data into event integration payloads that are sent to external systems such as webhooks, SIEM, Slack, Teams, or Datadog.

The injected data can blend with legitimate output, potentially causing confusion, data corruption, or manipulation of the information received by these systems.

This could lead to misleading alerts, incorrect logging, or unauthorized data being processed by downstream systems, which may affect monitoring, incident response, or automated workflows.

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Detection Guidance

This vulnerability involves JSON injection through user-controlled tokens in event-integration templates, which can be detected by monitoring webhook, SIEM, Slack, Teams, or Datadog payloads for unexpected or malformed JSON fields that resemble injected key-value pairs.

Detection can involve inspecting logs or intercepted payloads for JSON structures containing suspicious or unexpected keys that do not conform to normal template output.

Since the vulnerability is triggered by authenticated members setting their display name to JSON metacharacters, commands or scripts that query user display names for suspicious characters or patterns could help identify potential exploitation attempts.

No specific detection commands are provided in the available resources.

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Mitigation Strategies

The primary mitigation step is to upgrade Bitwarden Server to version 2026.5.0 or later, where the vulnerability has been fixed by properly serializing user-controlled values before inserting them into templates.

This fix prevents JSON injection by ensuring that injected tags are serialized and escaped, making them harmless in the rendered payloads.

Until the upgrade can be applied, consider reviewing and restricting event integration templates that use user-controlled tokens such as #ActingUserName# or #UserName# to minimize exposure.

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Compliance Impact

The vulnerability allows authenticated members to inject arbitrary key-value pairs into JSON payloads sent to external integrations such as webhook, SIEM, Slack, Teams, or Datadog endpoints. This injection could lead to the inclusion of malicious or unauthorized data in these payloads, potentially compromising data integrity and security.

Such unauthorized data manipulation and potential data leakage could negatively impact compliance with standards and regulations like GDPR and HIPAA, which require strict controls over data integrity, confidentiality, and secure handling of personal and sensitive information.

However, the provided information does not explicitly discuss compliance impacts or specific regulatory consequences.

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