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By Date By Thread Security Advisory - "Cross-VM ASL INtrospection (CAIN)" From: antonio <antonio () barresi net>

Date: Wed, 05 Aug 2015 23:47:46 +0200

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi there We discovered a new attack vector against memory deduplication in Virtual Machine Monitors (VMM) where attackers can effectively leak randomized base addresses of libraries and executables in processes of neighboring Virtual Machines (VM). The details are described in the security advisory below and in our WOOT'15 paper: https://www.usenix.org/conference/woot15/workshop-program/presentation/barresi Several vendors were notified about this issue in the beginning of June. This issue has CVE-2015-2877 assigned. An overview can also be found here: http://www.antoniobarresi.com/security/cloud/2015/07/30/cain/ Best, Antonio Security Advisory - "Cross-VM ASL INtrospection (CAIN)" - ------------------------------------------------------- Date: July 30, 2015 Description - ----------- We discovered a new attack vector against memory deduplication in Virtual Machine Monitors (VMM) where attackers can effectively leak randomized base addresses of libraries and executables in processes of neighboring Virtual Machines (VM). The attack takes advantage of the well known memory deduplication side-channel [1, 2]. VMMs that perform memory deduplication enable malicious VMs to detect shared pages as deduplicated pages usually incur higher write times because of the required copy-on-write. Our attack relies on a combination of the available side-channel, the ASLR implementation characteristics and the existence of suitable pages with certain properties (see below). We found memory pages in Windows and Linux systems that allow a malicious VM to silently brute force all possible base addresses. These pages are mostly static, long-lived and their entropy is directly derived from the randomized base address of a library or executable, making it possible to probe for the right randomized base address. Our PoC attack against the default configuration of KVM breaks ASLR of a neighboring Windows Server 2012 (x86_64) VM in less than 5 hours. We estimate an attack against Linux based systems (x86_64) to take around 18 days (with the same configuration). We expect a more determined attacker to further reduce attack time. The attack time also depends on the memory available to an attacker (more memory reduces attack time). Note: the attacker only needs user rights within the attacking VM thus no root/Administrator/elevated privileges are required. Attack variants - --------------- It is important to note that although the availability of the mentioned pages is existential for the attack, different data or code pages might be suitable for CAIN-like attacks. We cannot exclude that other pages (data or code) might be used by attackers to leak randomized base addresses. Therefore all mitigations that aim at specific pages are only effective as long as no other pages are available to be misused by attackers. Impact - ------ A malicious attacker can reliably leak the randomized base addresses of libraries and the executable of a process within a neighboring VM thus completely bypassing ASLR. Affected VMMs (Side-channel) - ---------------------------- Verified: KVM (on Ubuntu Server 14.04.2 with Linux Kernel 3.16.1) Most probably also affected: - - All KVM versions with KSM (Kernel Same-Page Merging) - - VMware products with TPS (Transparent Page Sharing) enabled (NOT enabled by default) - - VirtualBox supporting Page Fusion - - Any other VMM that uses page based same content memory deduplication Not affected: - - Microsoft Hyper-V products (does not perform page sharing, see also [3]) Affected Operating Systems (Victims) - ------------------------------------ Verified: Windows Sever 2012 Datacenter (6.2.9200 Build 9200) Existence of suitable pages also verified on: Ubuntu Linux 14.04 x86_64 Most probably also affected: - - Most 64-bit and 32-bit x86 Windows operating systems - - Most 64-bit and 32-bit x86 GNU/Linux distributions - - Other operating systems like OpenBSD, FreeBSD, etc. as well Mitigation - ---------- - - Deactivation of memory deduplication. - - Improvement of ASLR in victim systems by increasing entropy. - - Increase of entropy in memory pages of processes that are mainly static, long-lived and that contain base addresses (or can be directly derived by them). - - Increase size of shared pages i.e., use large pages for deduplication (e.g., 2MB). Reducing entropy with larger pages takes much longer due to the increase in the memory requirements of the attacker. - - VMMs can try to detect if an attack is going on based on memory allocation and page fault characteristics. This requires further investigation. Information related to Windows systems - -------------------------------------- Windows operating systems seem to be the most feasible targets. Even under High-Entropy ASLR, entropy for DLL base addresses is 19-bits. This number of bits and everything below can reliably be brute forced through the memory deduplication side-channel. The pages that make the attack possible are the first PE file pages mapped into the virtual address space of a process. These pages are static except for the ImageBase field within the Optional Header. The ImageBase field will be updated with the run-time base address of the DLL. Attackers can use this page to reliably brute force the ImageBase field to recover the randomized run-time base addresses of specific DLLs. As Windows employs system-wide ASLR the recovered base addresses can be used in attacks against all processes. Mitigations: - - Increase of ASLR entropy for code pages (DLLs and executables) - - Increase of entropy within the first page of a mapped PE file (to mitigate the PoC attack vector) - - Elimination of all suitable pages Information related to Linux systems - ------------------------------------ Linux based operating systems usually make use of the GNU tool chain. In GNU based systems, ELF shared libraries are usually deployed as PIC (Position-Independent Code). Thus most code pages have the same content despite their randomized base address. However, some pages still exist that are mapped from the ELF file's disk image to memory that contain base address relocations (R_X86_64_RELATIVE). These pages can be used by attackers to brute force the base address of a shared library in memory (e.g, libc). We found pages within the GNU_RELRO segment to be suitable. An attack against Linux based x86_64 systems can take around 18 days (estimate) with 4GB of attacker memory when running on a default KVM VMM. With 8GB attacker memory we estimate an attack time of 8.7 days. Attacks against x86 32-bit systems take considerably less (around hours). As Linux employs process-wide ASLR the recovered base addresses still need to be linked to a specific process within a victim VM. Mitigation: - - Increase entropy within GNU_RELRO pages - - Elimination of all suitable pages Information related to KVM - -------------------------- We implemented a PoC against KVM that is able to reliably recover the ntdll.dll randomized base address of a x86_64 Windows Sever 2012 victim VM. The attack takes less than 5 hours with the default KVM configuration of a Ubuntu Server 14.04.2 (sleep_millisecs = 200). Increasing sleep_millisecs slows down the attack, but does not prevent it. The attack also works when multiple victim VMs are running on the same KVM (we tested it with up to 6 victim VMs). While increasing the number of running VMs, attack time increases as well. As the attack is made possible as a combination of the side-channel and of victim VM characteristics, mitigations can be implemented on the VMM or victim VM side. For VMMs we see 2 possible remedies: - - Deactivation of memory deduplication. - - Detection of ongoing attacks based on memory allocation and page fault characteristics. This needs to be further investigated. Slowing down detection and merging of same-content pages might also be partly effective as attack time will inevitably increase. Disvovered by: - -------------- Antonio Barresi, Kaveh Razavi, Mathias Payer, Thomas R. Gross References: - ----------- [1]: "Memory Deduplication as a Threat to the Guest OS" https://staff.aist.go.jp/c.artho/papers/EuroSec2011-suzaki.pdf [2]: "Security Implications of Memory Deduplication in a Virtualized Environment" http://www.cs.wm.edu/~hnw/paper/memdedup.pdf [3]: "Mastering Hyper-V 2012 R2 with System Center and Windows Azure" Section "Memory Resources", "Why Page Sharing Technologies Are Not Used with Hyper-V" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJVwoR6AAoJEIm5W8tenpzo5SAQAL8oo6wtQirwgFZQUGr+qu02 BafIYY20glwuc+9enuwNxyLaQU9M3kHxUDzfgvXRMnwZ+6Lrucn5ABRM0HaO5y9Z WhF4tbq/bfimo2qSUnCu1hj0Nx5OGzmIbfl+TigilitlD+kvnArYm4ZX8Qy5MpKi naythhRAA0Juw+zlIg5TgeyT0dhnuWMMYrxOI9ZmVTf7832q3i9LPEnT3rzSFpP0 C+Y9gQM3VJWithnt4Ef2fK2a62M9cSF4/YBzO+A1QRAYK94dufRBdUJUZUulud/e RpHs95+2BamKz3XqZElRWDsPQ/X4kr2xGpbe7t0SZ5hEmzQecrlrIFJUhKQ20mPw OIb9gN++3Ea5JVIR9yi0yjnye2TwPaDGHDowszEO+YQpFabNDP6O5NgY5/XL+zoO jmb2qDi2c6mmbuZTAopySryk5qUuyQDKHV/c9v2fJ2XMD6c9t6OWkJpf+65VPYCh nSDULNixX+hO+R8cDku/UpyWg/bfI6Esz2JKYRu1Y7rF+L5WZ0BPcfC/uZ/7AiAh Qs46eCRa63vcr3cwicKqIP0kHChb8QX1/DF0GkrVIk5p2/aO3GVwH+RPQ8wGYv4M 4WDmm0uLkmpvX+HmDWjhr4lu6C8Up+Z1FhUygq7a4DdrD0OF+tQhKAd96XCuvorx j8Au/ZwIjSkarPpuU2hM =+P1i -----END PGP SIGNATURE----- _______________________________________________ Sent through the Full Disclosure mailing list https://nmap.org/mailman/listinfo/fulldisclosure Web Archives & RSS: http://seclists.org/fulldisclosure/ By Date By Thread Current thread: Security Advisory - "Cross-VM ASL INtrospection (CAIN)" antonio (Aug 06) Re: Security Advisory - "Cross-VM ASL INtrospection (CAIN)" Артур Истомин (Aug 06)

antonio (Aug 06)