It was discovered that pyOpenSSL incorrectly handled memory when handling X509 objects. A remote attacker could use this issue to cause pyOpenSSL to crash, resulting in a denial of service, or possibly execute arbitrary code. This attack appears to be exploitable via Depends on the calling application and if it retains a reference to the memory. This vulnerability appears to have been fixed in 17.5.0.

If a user provided callback to setcookiegeneratecallback returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer.

Cookie values that are too long are now rejected.

If a user provided callback to settlsextservernamecallback raised an unhandled exception, this would result in a connection being accepted. If a user was relying on this callback for any security-sensitive behavior, this could allow bypassing it.

Unhandled exceptions now result in rejecting the connection.

Credit to Leury Castillo for reporting this issue.