AJAX Spider fails to start browser with ClassCastException

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Ben G

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Jun 2, 2026, 10:28:10 AM (2 days ago) Jun 2

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Hi,

I run the ZAP stable Docker image (2.17.0, digest: sha256:8770b23f9e8b49038f413cb2b10c58c901e5b6717be221a22b1bcab5c9771b8a) in a Gitlab CI environment (Amazon Linux EC2 instance running Docker).

When I use the command `./zap-baseline.py -t <BASE_URL> -d -j -r zap_report.html -J zap_report.json -z "-config ajaxSpider.numberOfBrowsers=2"` the AJAX spider regularly fails with:

1) [Guice/ErrorInCustomProvider]: ClassCastException: class Boolean cannot be cast to class String (Boolean and String are in module java.base of loader 'bootstrap')
  at ConfigurationModule.configure(ConfigurationModule.java:47)
      \_ installed by: CoreModule -> ConfigurationModule
  at CrawlerContext.<init>(CrawlerContext.java:33)
      \_ for 1st parameter
  at Crawler.<init>(Crawler.java:76)
      \_ for 1st parameter
  at CrawlTaskConsumer.<init>(CrawlTaskConsumer.java:27)
      \_ for 3rd parameter
  while locating CrawlTaskConsumer

This doesn't always seem to fail this way, but it is more common than not. After this point, sometimes the job will succeed regardless (with the AJAX spider finding 0 URL's), but often it causes the job to hang as it appears that the Crawljax threads are not stopped.

I do not provide a zap.yaml, so everything is default other than the command arguments.

I can provide a zap.log, but I don't seem to be able to attach it to this message. so please let me know how I can add it.