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 * How to patch Exchange Server for the Hafnium zero-day attack
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 * The Microsoft Exchange Server hack: A timeline
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News Analysis


WHY THE MICROSOFT EXCHANGE SERVER ATTACK ISN’T GOING AWAY SOON


FOR SOME VICTIMS, PATCHING AND PROPER FORENSICS WILL BE DIFFICULT, PLUS NEW
THREAT ACTORS ARE NOW EXPLOITING THE SAME EXCHANGE SERVER VULNERABILITIES.

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By Cynthia Brumfield

CSO | 10 March 2021 10:00


Thinkstock



On March 2, Microsoft revealed a critical cybersecurity offensive launched by a
foreign adversary against organizations in the United States. The company
attributed the attacks to a Chinese advanced persistent threat group it calls
Hafnium. Microsoft quickly announced patches for the four previously unknown
vulnerabilities in Exchange Server that the malicious actors had exploited. 

Reports circulated last week that the hackers compromised at least 30,000, and
likely hundreds of thousands, of unpatched Exchange servers. As a consequence,
incident responders are working around the clock responding to this latest
threat, which they consider an actual attack on public and government IT
infrastructure, unlike the still-ongoing, primarily espionage-oriented
SolarWinds hack.

[ Related reading: How to patch Exchange Server for the Hafnium zero-day attack
| Sign up for CSO newsletters. ]

The Biden Administration, already grappling with the fallout from the massive
SolarWinds hack, which became public in December and has been widely, although
not officially, attributed to Russian hackers, said it would take" a whole of
government response to assess and address the impact." Anne Neuberger, the
deputy national security adviser for cybersecurity, leads that effort.


EXCHANGE SERVER ATTACK TIMELINE

The sequence of events around the Exchange Server attack shows how concern about
its consequences has escalated.

January 3: The date researchers at security firm Volexity believes the
vulnerabilities were first exploited.

March 2: Microsoft announces the attack and releases patches.



March 3: The Cybersecurity and Infrastructure Security Agency (CISA) issued an
emergency directive ordering all federal agencies to disconnect Microsoft
Exchange products running on-premises and report back on their efforts by March
5. CISA also issued an outline of the tactics, techniques, and procedures (TTPs)
and the indicators of compromise (IOCs) used by the threat group and offered
guidance on how to mitigate Exchange Server vulnerabilities.



March 6: Microsoft issued a new update to its Microsoft Safety Scanner (or
Microsoft Support Emergency Response Tool, MSERT) tool to scan for web shells
deployed in the recent attacks.

March 8: CISA published a remediating Microsoft Exchange Vulnerabilities web
page, "strongly" urging all organizations to address the vulnerabilities
immediately.

March 9: CISA published two new resources -- a web page entitled Remediating
Networks Affected by the SolarWinds and Active Directory/M365 Compromise and
another page, CISA Insights: SolarWinds and Active Directory/M365 Compromise:
Risk Decisions for Leaders. CISA is encouraging affected organizations to follow
the guidance in these resources.

March 10: A proof of concept is published for the Exchange Server attack, giving
other cybercriminal group instructions for exploiting the vulnerabilities. ESET
announces that it has identified ten APT groups actively attacking Exchange
Servers with the technique.

Despite the warnings and available resources, victims of the Exchange Server
attack could suffer consequences for an extended time. Here’s why.




PATCHING EXCHANGE SERVER IS NOT ENOUGH

"The biggest issue is that [the vulnerabilities were] being exploited on a
wide-scale basis prior to the patches being available," Tyler Hudak, practice
lead, Incident Response at TrustedSec, tells CSO. "Even if on minute one of the
patches being deployed you had gone and applied them, there's still a chance
that your system could have been compromised. I think a lot of people are under
the impression that 'Oh, well, we patched them, we're ok.' Which really isn't
the case."

Steven Adair, president of Volexity, tells CSO that several tools and resources
can help organizations determine if they were compromised. "The big challenge
then comes for these organizations to figure out how serious a breach was once
they find the indicators of attack or compromise."

Given the magnitude of the number of servers involved, remediation of the flaws
is a significant task that will undoubtedly cause operational disruption to vast
swaths of government and industry. "One challenge for some organizations in
responding to the Exchange vulnerabilities is that patching Exchange servers may
be time-consuming, especially if they are behind on patches, and it may require
downtime," Katie Nickels, director of intelligence at threat intelligence
cybersecurity firm Red Canary, tells CSO.


CYBERSECURITY TEAMS ARE TIRED

The double whammy of the SolarWinds breach and now the Exchange Server attacks
comes at a time when most cybersecurity professionals work more than full-time
to manage the mounting number of daily cybersecurity threats, including rapidly
rising cases of ransomware. "The fact that the SolarWinds and Exchange incidents
happened a few months apart, however, is significant because it means many
cybersecurity teams are tired," Nickels says. "For some organizations, response
to the SolarWinds compromise may still be ongoing, and now teams are hit with
potentially responding to Exchange compromises."



Even after the Microsoft patches are implemented, "you still have to go in, and
you still have to look for those indicators of compromise on your Exchange
servers to see if they were compromised," Hudak says. "What we've seen in our
investigations is that even prior to the patch being applied, if a server was
compromised, there was likely a backdoor uploaded to the server. The patch is
not going to prevent the backdoor from being accessed. The backdoor is
completely separate from the vulnerability."

Nickels agrees. "Installing these patches won't let you know if you've already
been compromised, let alone remediate an active intrusion. If security teams can
gather visibility into process lineage and command line parameters associated
with the Windows IIS [Internet Information Services] worker process, then they
may be able to hunt or build detection for this and other Exchange web shell
activity."


REMEDIATION CAN BE COMPLICATED

Remediation is possible, but for some organizations, the process can be more
complicated. "At this point, most organizations likely saw one or more attacks
that placed a web shell on their Exchange servers," Volexity's Adair says.
"However, there is a good chance the attackers did not access the web shells,
and the breaches are fairly limited and can be remedied fairly easily.

"At the same time, a smaller set of organizations have had attackers access the
web shells, dump credentials, move laterally, and start taking further steps to
move well beyond their Exchange servers. This is where remediation gets a lot
trickier and can involve anything from removing some files and updating a
handful of passwords to rebuilding several servers and resetting every password
in the organization."


OTHER GROUPS NOW EXPLOITING EXCHANGE SERVER

Adding even further insult to injury is that other threat actors are piling on
to the vulnerabilities first exploited by Hafnium. Hudak says that around March
5, he started to see other groups aside from the Chinese hackers exploiting the
Exchange vulnerabilities. "We know that there's a different group because they
were using a different backdoor than the previous attackers did. They used
different backdoor names. There are other groups out there that are figuring out
how to exploit this chain of vulnerabilities."

The path to patching and remediation could become exponentially more problematic
if someone publishes proof of concept code for the attacks, which Hudak expects
will happen this week. "As soon as that happens, everybody's going to have it,
and everybody will be able to exploit it," he says.


MANY FIRMS LACK FORENSICS KNOW-HOW

In addition to patching and hunting for backdoors, incident responders should
make copies of any backdoors they find before deleting them because forensic
firms will want to look at them, Hudak advises.

"Making sure you save evidence can be key," Adair says. "For example, instead of
powering down a virtual machine and deleting it, we would recommend taking a
snapshot (with memory) and saving a copy of the system in its compromised
state."

Unfortunately, most organizations don't have the capability or forensic
knowledge to get in there and figure out what the attackers did with the
backdoor, Hudak maintains. "Many small- and medium-sized businesses might lack
the expertise to conduct a full investigation if significant adversary activity
occurred," Nickels says.

Another potentially fraught cybersecurity task is to return any affected systems
to their last known good state, which means restoring everything from a backup
before the system or systems got compromised. "No matter how good your forensic
analyst is, there's always a chance they could miss something, or the attacker
could have deleted something. Reverting to that known good backup will make sure
that there is nothing on there now," Hudak says.

At the minimum, every organization using an Exchange server should immediately
patch, even if circumstances make patching painful. It's easy to tell
organizations to patch, but particularly if they are behind on Exchange updates,
this may not be a straightforward process," Nickels says. "Fortunately,
Microsoft has provided mitigation guidance for organizations who cannot patch.
Still, any organization running their own Exchange server should make immediate
patching a priority. The longer an unpatched server is connected to the
internet, the greater the risk is that it will be compromised."

Editor's note: This article has been updated on March 11 to include information
on the exploit's proof of concept.

More on cyberattacks:

 * Recent cyberattacks show disturbing trends
 * 11 types of hackers and how they will harm you
 * 5 signs you've been hit with an APT

Next read this
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Related:
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