There is memory leak and it can be repeated very easily, so it should be very easy to catch
Install Geronimo and then run some kind of benchmarking software against its admin UI login page, for example
program ab from Apache HTTP. This is realistic attack scenario, because lot of denial of service attacks are doing this (requesting one page many times).
Watching memory used graph in admin console shows free memory slowly decreasing. After all available memory is exhausted, application server stops serving new requests and never restores ifself back to working state.
I think that it is caused by allocating sessions without limiting total number of sessions to keep in memory and possibly to swap sessions out to file. There needs to be user-configurable setting for preventing this, it would be nice to add such setting to Admin console.
Its very important to get this bug fixed.