Teeworlds up to and including 0.7.5 is vulnerable to Buffer Overflow. A map parser does not validate m_Channels value coming from a map file, leading to a buffer overflow. A malicious server may offer a specially crafted map that will overwrite client's stack causing denial of service or code execution.
No fix upstream as of yet.
There is now a patch: https://github.com/teeworlds/teeworlds/commit/7e81ae1aac5dc4dc80b064262a4cef57d1361ce4