The US Cyber Command, the military agency tasked with US online operations, has warned companies and government agencies that malware linked to state-sponsored groups from Iran uses a flaw in Microsoft's Outlook mail client to turn off security features and gain access to users' credentials.
The vulnerability, patched in October 2017 by Microsoft, continues to be a threat because many companies do not regularly patch their systems. The last attacks used the vulnerability less than three weeks ago, says Nick Carr, senior manager investigating adversary methods at security service provider FireEye.
In addition, there are some signs that the patch, which turned off the vulnerable feature in Outlook, could be reversed by attackers, he says.
"This is a really interesting infection vector that we think will continue to be an issue," Carr says. "We are aware of, and our red team and other red teams have exploited, the brittleness of this patch. It can basically be disabled by modifying the registry key to roll back the patch entirely."
The warning comes as political tensions between the Trump administration and Iran continue to ratchet up, with both sides claiming to have launched cyberattacks against the other nation's networks. Security experts have linked the use of the Outlook exploit to two Iranian-sponsored groups, known as APT34, which attacks targets in the Middle East, and APT33, which targets organizations in the US, Europe, and the Middle East.
With Iran willing and able to use destructive malware, such as the data-destroying Shamoon attack, companies need to bolster their defenses, says Brandon Levene, head of applied intelligence at Chronicle, the threat intelligence arm of Alphabet, Google's parent company.
"Patch your systems or at least mitigate the outward access of these systems against exploitation if you cannot patch," he says. "The second is that understand if you are a viable target for Iranian interests, then these are things you need to understand as part of your threat models."
The Outlook flaw allows attackers to use the home page feature of the e-mail client to inject their own HTML and VisualBasic code, escaping from the secure sandbox. The vulnerability, CVE-2017-11774, can be triggered remotely, according to security firm SensePost, which discovered the flaw and reported it to Microsoft.
"This does have the downside of not allowing you to easily trigger the home page straight away, but you gain a stealthy persistence method," SensePost stated in its analysis. "I can also recommend you build some 'shell checks' into your exploit, as the home page gets cached by Outlook, so the exploit may trigger even after you have unset the home page value."
While 20 months should be enough time for a company to fix such a flaw, often such issues slip through the security process. The attack has been in use by Iran since at least 2018, security experts say.
On Tuesday USCYBERCOM submitted five files to VirusTotal that the military agency identified as part of an ongoing attack targeting a vulnerability in Microsoft Outlook patched in a regularly scheduled fix in October 2017.
"USCYBERCOM has discovered active malicious use of CVE-2017-11774 and recommends immediate #patching," the organization stated on Twitter. "Malware is currently delivered from: 'hxxps://customermgmt.net/page/macrocosm' #cybersecurity #infosec"
It's the first time USCYBERCOM has warned companies of a non-Russian attack, Levene says.
Some of the files used in the attack date back to 2016 and 2018. The malicious website, however, is as recent as a couple of weeks. Overall, the warning by USCYBERCOM is not very timely but gives a sense of what the military considers a threat, Levene says.
"Are these technical indicators really useful? Not really," he says. "These are historical indicators. It does set an interesting precedent for allowing us to get a better idea of the TTPs [tactics, techniques, and procedures] and behavior sets that CYBERCOM believes, at least, are relevant even now."