CVE-2009-3555 identifies a fundamental vulnerability in the TLS and SSL protocol implementations that affects Apache Tomcat and numerous other web server technologies through improper renegotiation handshake handling. This vulnerability, known as the "Project Mogul" issue, enables man-in-the-middle attackers to perform plaintext injection attacks by inserting data into HTTPS sessions during TLS renegotiation processes. The vulnerability details reveal that affected systems fail to properly associate renegotiation handshakes with existing connections, creating substantial exploit risk for secure communications. Apache Tomcat versions 7.0.0 through 7.0.9, 6.0.0 through 6.0.31, and 5.0.0 through 5.5.32 are vulnerable, along with Microsoft IIS 7.0, Apache HTTP Server 2.2.14 and earlier, OpenSSL before 0.9.8l, GnuTLS 2.8.5 and earlier, and Mozilla NSS 3.12.4 and earlier, demonstrating widespread impact across multiple technologies and vendors. The technical root cause lies in the TLS/SSL protocol's flawed renegotiation mechanism, where servers process unauthenticated requests retroactively in a post-renegotiation context, allowing attackers to inject malicious data into supposedly secure sessions. Known exploited vulnerabilities of this type target HTTPS communications and other TLS-protected sessions, with an EPSS score of 88.7 percentile indicating significant exploitation probability despite the protocol-level nature of the flaw. The vulnerability affects over 50 packages and libraries across Java, NGINX, and numerous other technologies, highlighting the fundamental nature of this cryptographic protocol weakness. Mitigation steps for Apache Tomcat include upgrading to versions 7.0.10, 6.0.32, or 5.5.33 and later, which implement workarounds for the TLS renegotiation issue. Organizations should prioritize updating all affected TLS/SSL implementations, disable TLS renegotiation where possible, and maintain updated CVE database records to track similar cryptographic protocol vulnerabilities that could compromise secure communications across web applications and network services.