Feeds

Microsoft gives temporary fix for info leak in ASP.Net

'Padding oracle' muzzled

Choosing a cloud hosting partner with confidence

Microsoft has issued a temporary fix for a cryptographic weakness in widely used web development software that allows attackers to read password files and other sensitive data.

The workaround issued late Friday addresses what is known as a “cryptographic padding oracle” in ASP.Net, a series of web development programs that run on top of Microsoft's Internet Information Services, or IIS. The weakness, which was demonstrated last week at the Ekoparty conference in Argentina, makes it possible for outsiders to read or tamper with sensitive data that is supposed to remain encrypted.

In cryptography parlance, an oracle is something that unintentionally reveals subtle clues about the encrypted contents. The vulnerability in ASP.Net can be exploited by sending a server huge numbers of queries and then analyzing the differing error messages that result. By repeating the process over and over, attackers can read the ASP.Net View State, which is used to keep track of changes made to web forms. The View State page, which can be used to store passwords, database connection strings and other sensitive data, is supposed to remain unreadable.

By tricking ASP.Net into revealing hints about the padding used to encrypt the data, attackers can eventually read or tamper with encrypted data sitting on a server running the web applications.

Microsoft on Friday acknowledged the vulnerability and said its security team was working on a patch that would plug the information disclosure hole.

In the meantime, ASP.Net users should run a script that will identify whether their systems are vulnerable. Systems that test positive should be reconfigured so that all error messages are mapped to a single error page that prevents the attacker from distinguishing among different types of errors, effectively muzzling the oracle.

Researchers Thai Duong and Juliano Rizzo last week demonstrated a point-and-click tool called POET, short for Padding Oracle Exploitation Tool, that has been updated to decrypt cookies, view states, form authentication tickets, and other sensitive data encrypted by ASP.Net. The video below provides a demonstration of the attack. ®

Internet Security Threat Report 2014

More from The Register

next story
FYI: OS X Yosemite's Spotlight tells Apple EVERYTHING you're looking for
It's on by default – didn't you read the small print?
Russian hackers exploit 'Sandworm' bug 'to spy on NATO, EU PCs'
Fix imminent from Microsoft for Vista, Server 2008, other stuff
Edward who? GCHQ boss dodges Snowden topic during last speech
UK spies would rather 'walk' than do 'mass surveillance'
Microsoft pulls another dodgy patch
Redmond makes a hash of hashing add-on
'LulzSec leader Aush0k' found to be naughty boy not worthy of jail
15 months home detention leaves egg on feds' faces as they grab for more power
China is ALREADY spying on Apple iCloud users, claims watchdog
Attack harvests users' info at iPhone 6 launch
Carders punch holes through Staples
Investigation launched into East Coast stores
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
Three 1TB solid state scorchers up for grabs
Big SSDs can be expensive but think big and think free because you could be the lucky winner of one of three 1TB Samsung SSD 840 EVO drives that we’re giving away worth over £300 apiece.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.