GHSA-6wf9-jmg9-vxcc

### Impact
The vulnerability may allow a remote attacker to allocate 100% CPU time on the target system depending on CPU type or parallel execution of such a payload resulting in a denial of service only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.

### Patches
XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

### Workarounds
See [workarounds](https://x-stream.github.io/security.html#workaround) for the different versions covering all CVEs.

### References
See full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for [CVE-2021-39140](https://x-stream.github.io/CVE-2021-39140.html).

### Credits
The vulnerability was discovered and reported by Lai Han of nsfocus security team.

### For more information
If you have any questions or comments about this advisory:
* Open an issue in [XStream](https://github.com/x-stream/xstream/issues)
* Contact us at [XStream Google Group](https://groups.google.com/group/xstream-user)