“SSL Death Alert” vulnerability
During an SSL or TLS handshake in OpenSSL, the client can repeatedly send packed undefined plaintext warning packets of SSL3_RT_ALERT -> SSL3_AL_WARNING. OpenSSL code ignores the undefined warning packets and continues processing subsequent communication content.
Attackers can exploit the vulnerability to pack many undefined warning packets in a single message. Then, the service or process falls in a meaningless cycle, resulting in 100% CPU usage. This vulnerability affects Nginx that widely provides the HTTPS (including SSL and TLS) service on the Internet.
- OpenSSL All 0.9.8
- OpenSSL All 1.0.1
- OpenSSL 1.0.2 through 1.0.2h
- OpenSSL 1.1.0
Unaffected versions: OpenSSL 1.0.2i, 1.0.2j, 1.1.0a, and 1.1.0b
How to fix or mitigate
Upgrade OpenSSL to the latest version:
- Upgrade OpenSSL 1.1.0 to OpenSSL 1.1.0b or a later version.
- Upgrade OpenSSL 1.0.2 to OpenSSL 1.0.2j or a later version.
- Upgrade OpenSSL 1.0.1 to OpenSSL 1.0.2 or a later version.