Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Network Security

6/26/2019
07:35 AM
Larry Loeb
Larry Loeb
Larry Loeb
50%
50%

Developers Find Temporary Fix for OpenSSH Remote Access Software Vulnerability

The latest update from the OpenSSH developers encrypts private keys before storing them into the system memory, which will protect the keys against almost all types of side-channel attacks.

Researchers keep coming up with memory side-channel vulnerabilities in modern processors and DRAMs, like Rowhammer, RAMBleed, Spectre and Meltdown. All of these attacks bypass architectural safeguards that are supposed to keep data behind an unscalable wall. The attacks act to infer memory-resident data that is being stored in plaintext for operational reasons.

Now, many researchers have demonstrated their side-channel attacks against the OpenSSH application installed on a targeted computer. This is because OpenSSH keeps a copy of your SSH key available in memory for multiple connections to the same remote server in a session.

OpenSSH is used to remotely access and manage computer systems and servers, and also for other automated machine-to-machine communications. While first designed for OpenBSD, it's also used by default in most Linux distributions today as well as being supported in Windows 10.

The latest update from the OpenSSH developers introduces a new security feature designed to mitigate this problem. It encrypts private keys before storing them into the system memory, which will protect the keys against almost all types of side-channel attacks.

Damien Miller said in the release notes for the update that, "This change encrypts private keys when they are not in use with a symmetric key that is derived from a relatively large 'prekey' consisting of random data (currently 16KB). Attackers must recover the entire prekey with high accuracy before they can attempt to decrypt the shielded private key, but the current generation of attacks have bit error rates that, when applied cumulatively to the entire prekey, make this unlikely. Implementation-wise, keys are encrypted 'shielded' when loaded and then automatically and transparently unshielded when used for signatures or when being saved/serialized."

The team is not looking to make this approach permanent. Indeed, they said that, "Hopefully we can remove this in a few years' time when computer architecture has become less unsafe."

There are limitations to what the developers have come up with. As they state in their patch notes, the technique makes successful side-channel attacks less likely, but not impossible.

The hardware that makes speculative and side-channel attacks possible in the first place will have to change in the future. But, even after that change, there will be legacy computers out there that will remain vulnerable to these kinds of attacks. Anything that can be done to deal with these compromised hardware designs now will have long-lasting effects on the security landscape.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Commentary
What the FedEx Logo Taught Me About Cybersecurity
Matt Shea, Head of Federal @ MixMode,  6/4/2021
Edge-DRsplash-10-edge-articles
A View From Inside a Deception
Sara Peters, Senior Editor at Dark Reading,  6/2/2021
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
The State of Cybersecurity Incident Response
In this report learn how enterprises are building their incident response teams and processes, how they research potential compromises, how they respond to new breaches, and what tools and processes they use to remediate problems and improve their cyber defenses for the future.
Flash Poll
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2021-34682
PUBLISHED: 2021-06-12
Receita Federal IRPF 2021 1.7 allows a man-in-the-middle attack against the update feature.
CVE-2021-31811
PUBLISHED: 2021-06-12
In Apache PDFBox, a carefully crafted PDF file can trigger an OutOfMemory-Exception while loading the file. This issue affects Apache PDFBox version 2.0.23 and prior 2.0.x versions.
CVE-2021-31812
PUBLISHED: 2021-06-12
In Apache PDFBox, a carefully crafted PDF file can trigger an infinite loop while loading the file. This issue affects Apache PDFBox version 2.0.23 and prior 2.0.x versions.
CVE-2021-32552
PUBLISHED: 2021-06-12
It was discovered that read_file() in apport/hookutils.py would follow symbolic links or open FIFOs. When this function is used by the openjdk-16 package apport hooks, it could expose private data to other local users.
CVE-2021-32553
PUBLISHED: 2021-06-12
It was discovered that read_file() in apport/hookutils.py would follow symbolic links or open FIFOs. When this function is used by the openjdk-17 package apport hooks, it could expose private data to other local users.