If a user provided callback to set_cookie_generate_callback 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 set_tlsext_servername_callback 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.
The X509Extension in pyOpenSSL before 0.13.1 does not properly handle a \0 character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.
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.
It was discovered that pyOpenSSL incorrectly handled memory when performing operations on a PKCS #12 store. A remote attacker could possibly use this issue to cause pyOpenSSL to consume resources, resulting in a denial of service. This attack appear to be exploitable via Depends upon calling application, however it could be as simple as initiating a TLS connection that would cause the calling application to reload certificates from a PKCS …