OpenSSL to fix the second critical flaw ever

The flaw (CVE-2014-0160, widely known as 'Heartbleed') is an out-of-bounds read (CWE-125) in the TLS and DTLS implementations of OpenSSL, caused by improper handling of Heartbeat Extension packets. A remote, unauthenticated attacker triggers it by sending a crafted heartbeat request whose declared payload length exceeds the data actually sent, causing OpenSSL to copy up to roughly 64 KB of adjacent process memory into the response. The attacker gains chunks of process memory per request — potentially TLS private keys, session cookies, usernames and passwords — and can repeat the request to harvest more, typically without any trace in logs. Any server or client running a vulnerable OpenSSL release that enables TLS or DTLS heartbeats is affected, which at the time of disclosure included hundreds of thousands of internet-exposed HTTPS servers as well as appliances, load balancers, and bundled libraries. Exploitation is confirmed in the wild: the vulnerability is listed in CISA KEV (added 2022-05-04, required action: apply updates per vendor instructions) and EPSS assigns it the maximum 100% probability of exploitation within 30 days.

Do: Apply OpenSSL updates per your OS or vendor's instructions — the upstream fix at the time of the 2014 disclosure was OpenSSL 1.0.1g, with most distributions shipping backported patches — and restart or rebuild every service linked against OpenSSL, including bundled copies in load balancers, appliances, and VPN or management interfaces. Because leaked memory can include TLS private keys, treat keys and certificates on affected endpoints as compromised: rotate keys, reissue and revoke certificates, and invalidate session cookies and credentials that may have leaked. Confirm the heartbeat fix is present on all TLS/DTLS endpoints to satisfy the CISA KEV required action.