Prosody before 0.10.0 allows remote attackers to cause a denial of service (application crash), related to an incompatibility with certain versions of the LuaSocket library, such as the lua-socket package from Debian stretch. The attacker needs to trigger a stream error. A crash can be observed in, for example, the c2s module.
https://www.debian.org/security/2018/dsa-4198
https://prosody.im/issues/issue/987
https://hg.prosody.im/0.9/rev/adfffc5b4e2a