Less than a week after it was revealed by UK-based Akamai security researcher Stephane Chazelas, the threat posed by the newly discovered Shellshock vulnerability – said by some to be “bigger than Heartbleed” – is still being reassessed as security experts around the world zero in on the recently discovered Bash shell flaw and the extent of the world's exposure to the bug becomes clear.
Discovered in a shell component that is widely used across Mac OS X, Linux and other versions of Unix, Shellshock (given a 10 out of 10 severity rating in the US National Vulnerability Database and officially catalogued as CVE-2014-7169) allows the ubiquitous shell command-line parser to tricked into executing arbitrary commands fed to it by a malicious outsider.
Shellshock is particularly problematic for users of CGI (Common Gateway Interface), widely used for generating dynamic Web content, because CGI can be exploited to run “any malicious command tacked-on to it”, Symantec warned in an explainer blog in which security analysts warned that “the consequences of an attacker successfully exploiting this vulnerability on a Web server are serious in nature”.
Pairing Shellshock with another vulnerability capable of escalating user privileges would “completely compromise an affected server”, Trend Micro security analysts warned in a blog on the subject.
Attackers may be able to dump password files or download malware onto infected computers, for example – and from there could “compromise and infect” other networked computers. This exposure is magnified in the Internet of Things (IoT) context because many embedded devices are based on Unix variants that involve running Bash.
“Businesses, in particular website owners, are most at risk from this bug and should be aware that its exploitation may allow access to their data and provide attackers with a foothold on their network,” the Symantec advisory warns. “Accordingly, it is of critical importance to apply any available patches immediately.”
Trend Micro security analysts warned that Bitcoin Core may be a “very attractive target to attackers” because it is controlled by Bash. With more than half the servers on the Internet running Linux and Google's Android based on the platform – and therefore also vulnerable – the Trend Micro team's analysis noted that the issue “is urgent and should be addressed immediately”.
“This bug is widespread, has the potential to do significant damage, and requires little-to-no technical knowledge to exploit,” the researchers warned.
Malware authors were jumping onboard with new exploits such as ELF_BASHLITE.A, which is capable of launching potentially damaging distributed denial-of-service (DDoS) attacks. Exploit attempts were continuing in China and, with an estimated 10 percent of desktops and laptops worldwide at risk, many were arguing that the issue was likely to get worse before it gets better.
Ongoing analysis of the bug was revealing further vulnerabilities: Google security researcher Michal Zalewski, for one, was updating the Twitter world and blogging about his work examining the bug and as of Monday had identified the “6th and most serious issue” in Bash.
Vendors were racing to keep their patches up to date as the vulnerability continued to be exploited. “The good news is that this vulnerability was disclosed responsibly,” Palo Alto Networks researchers warned in a security update from that company. “The bad news is that this vulnerability is going to have a very long tail.”
Exposure to the bug would ultimately vary according to the target's use of Unix and Mac OS X, experts agreed.
“As more common Web frameworks are analysed, I would suspect more targeted attacks to be forthcoming,” Blue Coat senior vice president and chief security strategist wrote in an advisory.
“It all depends on server configurations and if fields are passed as a variable on the command line. As more common web frameworks are analysed, I would suspect more targeted attacks to be forthcoming.”
Many users might have the issue fixed quickly through automatic application of vendor patches, he added, but it was important to check: "there is already a patch out for the nasty bug," he wrote, "and if you have automatic updates configured there is a good chance it may already be installed. However, I wouldn't bet your server on it.”
This article is brought to you by Enex TestLab, content directors for CSO Australia.
Read more: Six key defenses against Shellshock attacks