Security mavens bracing for Thursday's scheduled disclosure of a high-severity vulnerability in the widely used OpenSSL crypto library need wait no longer. It's a bug that allows end users to crash servers running one version of the software by sending data that's relatively easy to duplicate.

"If a client connects to an OpenSSL 1.0.2 server and renegotiates with an invalid signature algorithms extension, a NULL pointer dereference will occur," an advisory published Thursday morning stated. "This can be exploited in a DoS attack against the server."

CVE-2015-0291, as the vulnerability is indexed, struck many people as anticlimactic, given Monday's advisory that a "high" severity bug would be announced. That triggered concerns of a critical bug along the lines of the highly critical Heartbleed vulnerability that attackers used to extract passwords, private keys, and other confidential data from servers used for banking, shopping, and e-mail. By comparison, Thursday's DoS bug can be used only to force a vulnerable server to reboot.

The vulnerability was widely discussed earlier this week in social media threads such as this one. It was discovered by David Ramos of Stanford University, who agreed to withhold publishing proof-of-concept code that exploits the bug until server administrators have had time to patch the security hole. Based on today's description of the bug, however, it likely won't be hard for other people to independently develop exploits.

FREAK gets reclassified

Thursday's advisory also reclassified as "high" an advisory for FREAK, a bug that causes many servers to offer 512-bit encryption keys that can be broken for about $100 each, or for just pennies per server in extreme cases. From there, attackers were free to carry out man-in-the-middle attacks on traffic between vulnerable servers and end users. The weak keys were the result of 1990s export controls the Clinton administration placed on strong cryptography. Many engineers abandoned the regimen once the restrictions were dropped, but somehow the ciphers have managed to live on a select but significant number of end-user devices and servers. OpenSSL maintainers previously rated the severity of CVE-2015-0204 as low.

"This was classified low because it was originally thought that server RSA export ciphersuite support was rare," Thursday's advisory stated. "A client was only vulnerable to a MITM attack against a server which supports an RSA export ciphersuite. Recent studies have shown that RSA export ciphersuites support is far more common."

Administrators responsible for servers that rely on OpenSSL—whether for websites, e-mail, virtual private networks, or other applications—should pay close attention to the advisory, since it outlines 11 other vulnerabilities besides the DoS and reclassified FREAK weaknesses. The rest of us can go about our business, confident that none of them come close to the severity of Heartbleed.