Siemens has fixed bugs in its Simatic S7 industrial computer systems, used to control machines on factory floors, power stations and chemical plants.
The patches, released Friday, mark Siemens' first response to a high-profile computer security incident since the Stuxnet worm, which was discovered a year ago circulating on computer networks in Iran.
Siemens fixed a pair of flaws in the S7-1200 controller, acknowledging that one could be leveraged to take control of the system using what's known as a replay attack. A second flaw, in a Web server that ships with the device, could give attackers a way to crash the system. However, the attacker would have to first find a way onto the victim's network before launching these attacks.
Siemens had been scrambling to fix the bugs since they were discovered earlier this year by Dillon Beresford, a researcher with security vendor NSS Labs. Beresford had hoped to discuss the issues at a May hacking conference in Dallas, but pulled out of the event when it became clear that Siemens could not fix the problem in time.
His company said that talking about the bugs was too risky and decided instead to disclose the issues in August at the Black Hat security conference.
In an interview Friday, Beresford said it wasn't clear how many of the six vulnerabilities he'd discovered had been patched. That will require further testing. He said the replay attack that Siemens patched Friday is one of the most serious of the bugs, but there is at least one other equally serious problem that may not yet be fixed.
The U.S. Department of Homeland Security said that Siemens' patches fix "a portion" of the problems Beresford has discovered and that it "continues to work with Siemens and Mr. Beresford on the other reported problems."
Siemens seemed to downplay the severity of the issues -- something it has done in the past. In its security advisory, the company noted that Beresford's research was done in "laboratory conditions and without any IT security measures in place."
On its website, the company said that the denial-of-service attack did not affect its S7-300 and S7-400 controllers, but Siemens didn't say whether these devices are vulnerable to the replay attack. "We are currently testing all systems including S7-300 and 400 in replay scenarios," a Siemens spokesman said Friday via e-mail. "Depending on the results of those tests, we will have to react accordingly."
Beresford says that the 300 and 400 models could also be hit by this attack and the replay attack is more serious than the Siemens advisory would lead one to believe -- an attacker could take "full control" over the Siemens system.
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