A vulnerability, which was classified as very critical, has been found in DRAM. Affected by this issue is an unknown functionality of the component PTE Handler. The manipulation with an unknown input leads to a privileges management vulnerability (Rowhammer). Using CWE to declare the problem leads to CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. Impacted is confidentiality, integrity, and availability.

The weakness was presented 03/09/2015 by Mark Seaborn, Matthew Dempsky and Thomas Dullien as Exploiting the DRAM rowhammer bug to gain kernel privileges as confirmed posting (Blog). The advisory is shared for download at googleprojectzero.blogspot.ch. This vulnerability is handled as CVE-2015-0565 since 01/06/2015. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are unknown but a public exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 04/12/2022). The MITRE ATT&CK project declares the attack technique as T1068. This vulnerability has a historic impact due to its background and reception. The advisory points out:

“Rowhammer” is a problem with some recent DRAM devices in which repeatedly accessing a row of memory can cause bit flips in adjacent rows. We tested a selection of laptops and found that a subset of them exhibited the problem. We built two working privilege escalation exploits that use this effect. One exploit uses rowhammer-induced bit flips to gain kernel privileges on x86-64 Linux when run as an unprivileged userland process. When run on a machine vulnerable to the rowhammer problem, the process was able to induce bit flips in page table entries (PTEs). It was able to use this to gain write access to its own page table, and hence gain read-write access to all of physical memory.

A public exploit has been developed in Assembler and been published immediately after the advisory. The exploit is available at googleprojectzero.blogspot.ch. It is declared as proof-of-concept. As 0-day the estimated underground price was around $100k and more. The code used by the exploit is:

code1a:
  mov (X), %eax  // Read from address X
  mov (Y), %ebx  // Read from address Y
  clflush (X)  // Flush cache for address X
  clflush (Y)  // Flush cache for address Y
  jmp code1a

As DRAM manufacturing scales down chip features to smaller physical dimensions, to fit more memory capacity onto a chip, it has become harder to prevent DRAM cells from interacting electrically with each other. As a result, accessing one location in memory can disturb neighbouring locations, causing charge to leak into or out of neighbouring cells.

The best possible mitigation is suggested to be Workaround. The posting contains the following remark:

There are signs that some newer hardware implements mitigations.

The vulnerability is also documented in the databases at X-Force (101427) and Exploit-DB (36310). news.softpedia.com is providing further details.

Affected

• All Products using DRAM
• Confirmed: Cisco Unified Computing System B-Series Blade Servers
• Confirmed: Cisco Unified Computing System E-Series ISR Blade Servers
• Confirmed: Cisco Unified Computing System C-Series Rack Servers
• Confirmed: Cisco Nexus 3000
• Confirmed: Cisco Nexus 9000

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• DRAM

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