CVE-2026-52824

Kimai is an open-source time tracking application. Prior to 2.58.0, the official Docker image sets APP_SECRET to the public value change_this_to_something_unique in Dockerfile, and .docker/entrypoint.sh neither replaces nor rejects that value before Symfony uses it as kernel.secret. An unauthenticated attacker who reaches a deployment that did not override APP_SECRET, knows a username, correctly guesses the account ID associated with that username, and targets an account without active two-factor authentication can forge HMAC-protected authentication artifacts, including KIMAI_REMEMBER cookies and login links, to access the account without its password. The updated entrypoint generates and persists a random secret when no safe operator-provided value exists. This issue is fixed in version 2.58.0.

Kimai is an open-source time tracking application. Prior to 2.58.0, the official Docker image sets APP_SECRET to the public value change_this_to_something_unique in Dockerfile, and .docker/entrypoint.sh neither replaces nor rejects that value before Symfony uses it as kernel.secret. An unauthenticated attacker who reaches a deployment that did not override APP_SECRET, knows a username, correctly guesses the account ID associated with that username, and targets an account without active two-factor authentication can forge HMAC-protected authentication artifacts, including KIMAI_REMEMBER cookies and login links, to access the account without its password. The updated entrypoint generates and persists a random secret when no safe operator-provided value exists. This issue is fixed in version 2.58.0.

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.

Kimai is an open-source time tracking application. Prior to 2.58.0, the official Docker image sets APP_SECRET to the public value change_this_to_something_unique in Dockerfile, and .docker/entrypoint.sh neither replaces nor rejects that value before Symfony uses it as kernel.secret. An unauthenticated attacker who reaches a deployment that did not override APP_SECRET, knows a username, correctly guesses the account ID associated with that username, and targets an account without active two-factor authentication can forge HMAC-protected authentication artifacts, including KIMAI_REMEMBER cookies and login links, to access the account without its password. The updated entrypoint generates and persists a random secret when no safe operator-provided value exists. This issue is fixed in version 2.58.0.

Kimai is an open-source time tracking application. Prior to 2.58.0, the official Docker image sets APP_SECRET to the public value change_this_to_something_unique in Dockerfile, and .docker/entrypoint.sh neither replaces nor rejects that value before Symfony uses it as kernel.secret. An unauthenticated attacker who reaches a deployment that did not override APP_SECRET, knows a username, correctly guesses the account ID associated with that username, and targets an account without active two-factor authentication can forge HMAC-protected authentication artifacts, including KIMAI_REMEMBER cookies and login links, to access the account without its password. The updated entrypoint generates and persists a random secret when no safe operator-provided value exists. This issue is fixed in version 2.58.0.

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.