Slack integration leaks sensitive information in logs

Impact

Sentry's Slack integration incorrectly records the incoming request body in logs. This request data can contain sensitive information, including the deprecated Slack verification token. With this verification token, it is possible under specific configurations, an attacker can forge requests and act as the Slack integration.

The request body is leaked in log entries matching event == "slack.*" && name == "sentry.integrations.slack" && request_data == *. The deprecated slack verification token, will be found in the request_data.token key.

Example event:

{
    "name": "sentry.integrations.slack",
    "level": "info",
    "event": "slack.event.message",  # This could be any of the `slack.*` events
    "request_data": {
      # Other keys are omitted for brevity
      "token": "<MyDeprecatedSlackVerificationToken>",
    }
}

Patches

• SaaS users do not need to take any action.
• Self-hosted users should upgrade to version 24.5.0 or higher, rotate their Slack verification token, and use the Slack Signing Secret instead of the verification token.
  • If you are only using the slack.signing-secret in your self-hosted configuration, then the legacy verification token is not used to verify the webhook payload. It is ignored.

⚠️ Sentry's support for validating Slack requests via the legacy verification token will be deprecated in version 24.7.0.

Workarounds

Option 1

Set the slack.signing-secret instead of slack.verification-token. The signing secret is Slack's recommended way of authenticating webhooks.

By having slack.singing-secret set, Sentry self-hosted will no longer use the verification token for authentication of the webhooks, regardless of whether slack.verification-token is set or not.

Option 2

The deprecated Slack verification token is leaked in log levels of INFO and ERROR in the Slack integration. If the self-hosted instance is unable to be upgraded or re-configured to use the slack.signing-secret, the logging configuration can be adjusted to not generate logs from the integration. The default logging configuration can be found in src/sentry/conf/server.py. Services should be restarted once the configuration change is saved.

Below you'll find an example of the configuration adjustments necessary to remove the Slack integration logs:

# src/sentry/conf/server.py

...
 
LOGGING: LoggingConfig = {
    ...
    handlers: {
        # the line below already exists in the default configuration
        "null": {"class": "logging.NullHandler"},
        ...
    },
    "loggers": {
        "sentry.integrations.slack": {
            "handlers": ["null"],  # route logs to null handler
            "level": "CRITICAL",  # prevent generation of logs a lower levels (ex. ERROR and INFO)
        },
        ...
    },
}

References

• https://github.com/getsentry/sentry/pull/70508
• Sentry Slack Integration Documentation for Self-Hosted users
• Documentation on Slack Signing Secrets
• Slack Deprecation for Verification Tokens