Feeds

iOS 7's weak random number generator stuns kernel security – claim

'Trivial' to break PRNG used to mitigate against attacks, says researcher

Remote control for virtualized desktops

In an effort to improve iDevice security, Apple replaced its internal random number generator between iOS 6 and iOS 7 – but a security researcher believes Cupertino inadvertently downgraded security.

The issue is outlined here by Azimuth Security, whose Tarjei Mandt also detailed the issue at last week's CanSecWest conference in Vancouver.

Mandt says the early_random() PRNG (pseudo-random number generator), shipped in the latest iOS 7 update, is “alarmingly weak”. According to ThreatPost, he told the conference the PRNG is “deterministic and trivial to brute force”.

The PRNG is started at boot time, and as Azimuth Security explains, it uses what's called a linear congruential generator (LCG) to provide entropy for the PRNG. The company's white paper explains the LRG thus:

“An LCG is an algorithm that yields a sequence of random numbers calculated with a linear equation. LCGs are one of the oldest and best-known pseudo-random number generator algorithms, and are commonly leveraged in standard libraries and applications for being fast and easy to implement. Although these algorithms perform well in resource-constrained environments and have appealing statistical properties, they exhibit some severe defects and are easily broken when confronted by an adversary who can monitor outputs”.

Mandt writes that the vulnerability could recover PRNG outputs “without being assisted by additional vulnerabilities or having prior knowledge about the kernel address space … this may allow trivial exploitation of vulnerabilities previously deemed non-exploitable”.

The early_random() in iOS 7, the company explains in its blog post, can only produce a maximum of 219 unique outputs, and after 217 outputs: the longest sequence of unique PRNG outputs, he writes, is just 131,072.

“An attacker can recover arbitrary outputs if the lower 19 bits of the internal state is known,” Mandt writes in his slide-pack (here). While the system discards the lower three bits of that state, these are trivial to recover from two successive states of the PRNG.

That means the PRNG seed generated at power-up by iBoot is recoverable, he writes.

“An unprivileged attacker, even when confined by the most restrictive sandbox, can recover arbitrary outputs from the generator and consequently bypass all the exploit mitigations that rely on the early random PRNG,” Mandt concludes. ®

Remote control for virtualized desktops

More from The Register

next story
Regin: The super-spyware the security industry has been silent about
NSA fingered as likely source of complex malware family
Why did it take antivirus giants YEARS to drill into super-scary Regin? Symantec responds...
FYI this isn't just going to target Windows, Linux and OS X fans
Privacy bods offer GOV SPY VICTIMS a FREE SPYWARE SNIFFER
Looks for gov malware that evades most antivirus
Home Office: Fancy flogging us some SECRET SPY GEAR?
If you do, tell NOBODY what it's for or how it works
Patch NOW! Microsoft slings emergency bug fix at Windows admins
Vulnerability promotes lusers to domain overlords ... oops
HACKERS can DELETE SURVEILLANCE DVRS remotely – report
Hikvision devices wide open to hacking, claim securobods
'Regin': The 'New Stuxnet' spook-grade SOFTWARE WEAPON described
'A degree of technical competence rarely seen'
Syrian Electronic Army in news site 'hack' POP-UP MAYHEM
Gigya redirect exploit blamed for pop-rageous ploy
prev story

Whitepapers

Designing and building an open ITOA architecture
Learn about a new IT data taxonomy defined by the four data sources of IT visibility: wire, machine, agent, and synthetic data sets.
Getting started with customer-focused identity management
Learn why identity is a fundamental requirement to digital growth, and how without it there is no way to identify and engage customers in a meaningful way.
10 threats to successful enterprise endpoint backup
10 threats to a successful backup including issues with BYOD, slow backups and ineffective security.
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.
10 ways wire data helps conquer IT complexity
IT teams can automatically detect problems across the IT environment, spot data theft, select unique pieces of transaction payloads to send to a data source, and more.