Old code, new exploits.
The worst breaches hit code everyone already trusted. Reviewed many times over, and still carrying a flaw for years. Age and reputation are not evidence. A check you can repeat at every release is.
8 bytes nobody questioned · exploited after years in production
Shellshock · Bash
A command-injection flaw sat in Bash for about 25 years; mass scanning began within hours of disclosure.
Heartbleed · OpenSSL
A missing bounds check in the main TLS library leaked server memory, private keys included, for two years.
Log4Shell · Log4j
A lookup feature added in 2013 let a single log line run remote code, in software nearly every Java team ran.
xz · liblzma
A backdoor reached release tarballs that did not match the public source. Nobody compared the bytes.
regreSSHion · OpenSSH
A bug fixed in 2006 came back in a 2020 release and opened unauthenticated root code execution.
Ronin · bridge
Five of nine validator keys were enough to sign withdrawals; about $600M left before anyone noticed.