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Kimai: Default APP_SECRET in Docker Image Enables Cookie Forgery and Account Takeover

Critical severity GitHub Reviewed Published Jun 11, 2026 in kimai/kimai • Updated Jul 14, 2026

Package

composer kimai/kimai (Composer)

Affected versions

<= 2.57.0

Patched versions

2.58.0

Description

Summary

The official Kimai Docker image ships with APP_SECRET=change_this_to_something_unique as the default environment variable. The Docker entrypoint does not override or validate this value. Any Kimai instance deployed using the Docker image without explicitly setting APP_SECRET runs with a publicly-known Symfony kernel.secret, enabling an unauthenticated attacker to forge HMAC-signed cookies and login links to take over any account including super_admin.

Details

Dockerfile:263 sets ENV APP_SECRET=change_this_to_something_unique. This value is consumed by config/packages/framework.yaml:7 as kernel.secret, which Symfony uses to HMAC-sign:

  • The KIMAI_REMEMBER remember-me cookie
  • LoginLink signatures
  • Password reset URLs
  • CSRF tokens

The .docker/entrypoint.sh does not check for or replace the default sentinel value. The bare-metal .env.dist:38 ships the same default. No startup-time guard exists anywhere in the codebase that refuses to start when APP_SECRET equals the sentinel.

User IDs are sequential integers starting from 1. The first super_admin account is almost always id=1. User IDs are visible in some URLs and API responses.

A PoC was provided, but removed for security reasons.

Impact

Any Kimai instance deployed via the official Docker image without overriding APP_SECRET can be compromised from the internet. An unauthenticated attacker who can reach the Kimai URL can forge authentication tokens and log in as any user if:

  • a username is known AND
  • the correct account ID for this username is guessed AND
  • the account has no active 2FA (two factor) authentication

Solution

  • The entrypoint.sh file is updated and now contains a script that generates a random APP_SECRET via bin2hex(random_bytes(32)) which will be stored in /opt/kimai/var/data/.appsecret
  • The entrypoint.sh will create the file /opt/kimai/.env.local containing the APP_SECRET, either fetched from the Docker Environment or from the newly created secret file
  • The documentation was updated to highlight the importance of using a random secret for APP_SECRET
  • The Dockerfile removed default APP_SECRET=change_this_to_something_unique
  • Login links now contain more entropy (see GHSA-m492-gv72-xvxj) - so even without all previous changes, attackers won't be able to generate Login links even for installations that have a hard-coded APP_SECRET=change_this_to_something_unique

See https://www.kimai.org/en/security/ghsa-jr9p-4h4j-6c58 for more information.

References

@kevinpapst kevinpapst published to kimai/kimai Jun 11, 2026
Published to the GitHub Advisory Database Jul 14, 2026
Reviewed Jul 14, 2026
Last updated Jul 14, 2026

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity High
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Initialization of a Resource with an Insecure Default

The product initializes or sets a resource with a default that is intended to be changed by the administrator, but the default is not secure. Learn more on MITRE.

CVE ID

CVE-2026-52824

GHSA ID

GHSA-jr9p-4h4j-6c58

Source code

Credits

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