ID

VAR-201409-1156

CVE

CVE-2014-6271

TITLE

GNU Bash shell executes commands in exported functions in environment variables

DESCRIPTION

GNU Bash through 4.3 processes trailing strings after function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution, aka "ShellShock." NOTE: the original fix for this issue was incorrect; CVE-2014-7169 has been assigned to cover the vulnerability that is still present after the incorrect fix. GNU Bash 4.3 and earlier contains a command injection vulnerability that may allow remote code execution. An attacker can exploit this issue to execute arbitrary code within the context of the affected application. Failed exploit attempts will result in a denial-of-service condition. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Note: the current version of the following document is available here: https://h20564.www2.hp.com/portal/site/hpsc/public/kb/ docDisplay?docId=emr_na-c04467807 SUPPORT COMMUNICATION - SECURITY BULLETIN Document ID: c04467807 Version: 2 HPSBGN03117 rev.2 - HP Remote Device Access: Virtual Customer Access System (vCAS) running Bash Shell, Remote Code Execution NOTICE: The information in this Security Bulletin should be acted upon as soon as possible. Release Date: 2014-09-30 Last Updated: 2014-11-11 Potential Security Impact: Remote code execution Source: Hewlett-Packard Company, HP Software Security Response Team VULNERABILITY SUMMARY A potential security vulnerability has been identified with HP Remote Device Access: Virtual Customer Access System (vCAS) running Bash Shell. NOTE: The vCAS product is vulnerable only if DHCP is enabled. References: CVE-2014-6271 CVE-2014-7169 SSRT101724 SUPPORTED SOFTWARE VERSIONS*: ONLY impacted versions are listed. All vCAS versions prior to 14.10-38402 BACKGROUND CVSS 2.0 Base Metrics =========================================================== Reference Base Vector Base Score CVE-2014-6271 (AV:N/AC:L/Au:N/C:C/I:C/A:C) 10.0 CVE-2014-7169 (AV:N/AC:L/Au:N/C:C/I:C/A:C) 10.0 =========================================================== Information on CVSS is documented in HP Customer Notice: HPSN-2008-002 RESOLUTION HP has made the following updates available to resolve the vulnerability in HP Remote Device Access: Virtual Customer Access System (vCAS) running Bash Shell. Customers should upgrade their vCAS systems using the web UI or the "casupdate" command. There are also new VirtualBox and VMware ESX images available: - VMware ESX/ESXi image: https://h20529.www2.hp.com/apt/hp-rdacas-14.10-38402.ova - VirtualBox image: https://h20529.www2.hp.com/apt/hp-rdacas-14.10-38402-vbox.ova NOTE: - HP recommends to not power-down or disconnect the vCAS until the update is available. - The vCAS pulls down the latest updates from HP by using Ubuntus apt-get facility. - HP does not push updates out on to the vCAS so customers will have to be proactive and install the latest updates. Actions Required The DHCP exploit can be mitigated by ensuring that DHCP is disabled on the vCAS as detailed in MITIGATION INFORMATION below. Download updates by using a web browser: 1. Connect to the vCAS and login as hp-admin 2. Go to Tools -> Software Updates 3. Under "Manual Actions" select Check now and then upgrade now See HP Remote Device Access vCAS User Guide, Chapter 4, Software Updates for more details: http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/action.pro cess/public/psi/manualsDisplay/?sp4ts.oid=4256914&javax.portlet.action=true&s pf_p.tpst=psiContentDisplay&javax.portlet.begCacheTok=com.vignette.cachetoken &spf_p.prp_psiContentDisplay=wsrp-interactionState%3DdocId%253Demr_na-c033816 86%257CdocLocale%253Den_US&javax.portlet.endCacheTok=com.vignette.cachetoken MITIGATION INFORMATION A Shellshock attack requires the definition of an environment variable introduced into Bash. The vCAS has three attack vectors: SSH, the lighttpd web server, and the DHCP client. - The exploit does not elevate privileges. The DHCP client uses Bash scripts and is vulnerable to Shellshock. The DHCP exploit can be mitigated by ensuring that DHCP is disabled on the vCAS. Note: HP strongly discourages the use of DHCP on the vCAS. The web UI forces the vCAS user to assign a static IP address and change the hp-admin password. A vCAS user must manually configure DHCP for use on the vCAS. A vCAS user can verify that DHCP is disabled by inspecting the file "/etc/network/interfaces" and ensuring that the "iface" line for device "eth0" is set for a static IP. Example of a static IP configuration: # The primary network interface auto eth0 iface eth0 inet static address 172.27.1.68 netmask 255.255.255.0 gateway 172.27.1.1 HISTORY Version:1 (rev.1) - 30 September 2014 Initial release Version:2 (rev.2) - 11 November 2014 Software updates available Third Party Security Patches: Third party security patches that are to be installed on systems running HP software products should be applied in accordance with the customer's patch management policy. Support: For issues about implementing the recommendations of this Security Bulletin, contact normal HP Services support channel. For other issues about the content of this Security Bulletin, send e-mail to security-alert@hp.com. Report: To report a potential security vulnerability with any HP supported product, send Email to: security-alert@hp.com Subscribe: To initiate a subscription to receive future HP Security Bulletin alerts via Email: http://h41183.www4.hp.com/signup_alerts.php?jumpid=hpsc_secbulletins Security Bulletin Archive: A list of recently released Security Bulletins is available here: https://h20564.www2.hp.com/portal/site/hpsc/public/kb/secBullArchive/ Software Product Category: The Software Product Category is represented in the title by the two characters following HPSB. 3C = 3COM 3P = 3rd Party Software GN = HP General Software HF = HP Hardware and Firmware MP = MPE/iX MU = Multi-Platform Software NS = NonStop Servers OV = OpenVMS PI = Printing and Imaging PV = ProCurve ST = Storage Software TU = Tru64 UNIX UX = HP-UX Copyright 2014 Hewlett-Packard Development Company, L.P. Hewlett-Packard Company shall not be liable for technical or editorial errors or omissions contained herein. The information provided is provided "as is" without warranty of any kind. To the extent permitted by law, neither HP or its affiliates, subcontractors or suppliers will be liable for incidental,special or consequential damages including downtime cost; lost profits; damages relating to the procurement of substitute products or services; or damages for loss of data, or software restoration. The information in this document is subject to change without notice. Hewlett-Packard Company and the names of Hewlett-Packard products referenced herein are trademarks of Hewlett-Packard Company in the United States and other countries. Other product and company names mentioned herein may be trademarks of their respective owners. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iEYEARECAAYFAlRiTVMACgkQ4B86/C0qfVkVXwCgnt3AiI6i2W/bYpzl1OdUS3V0 240AnAzsgVtgeyaCKxbE7+fRS74qViiq =Gpae -----END PGP SIGNATURE----- . HP Product Firmware Version HP StoreEver ESL G3 Tape Libraries with MCB version 2 680H_GS40701 HP StoreEver ESL G3 Tape Libraries with MCB version 1 656H_GS10801 The firmware is customer installable and is available in the Drivers, Software & Firmware section at the following location: http://www.hp.com/support/eslg3 Notes: - Updating the library firmware requires a reboot of the library. - If the library firmware cannot be updated, HP recommends following the Mitigation Instructions below. Good morning! This is kinda long. == Background == If you are not familiar with the original bash function export vulnerability (CVE-2014-6271), you may want to have a look at this article: http://lcamtuf.blogspot.com/2014/09/quick-notes-about-bash-bug-its-impact.html Well, long story short: the initial maintainer-provided patch for this issue [1] (released on September 24) is *conclusively* broken. After nagging people to update for a while [5] [7], I wanted to share the technical details of two previously non-public issues which may be used to circumvent the original patch: CVE-2014-6277 and CVE-2014-6278. Note that the issues discussed here are separate from the three probably less severe problems publicly disclosed earlier on: Tavis' limited-exploitability EOL bug (CVE-2014-7169) and two likely non-exploitable one-off issues found by Florian Weimer and Todd Sabin (CVE-2014-7186 and CVE-2014-7187). == Required actions == If you have installed just the September 24 patch [1], or that and the follow-up September 26 patch for CVE-2014-7169 [2], you are likely still vulnerable to RCE and need to update ASAP, as discussed in [5]. You are safe if you have installed the unofficial function prefix patch from Florian Weimer [3], or its upstream variant released on September 28 [4]. The patch does not eliminate the problems, but shields the underlying parser from untrusted inputs under normal circumstances. Note: over the past few days, Florian's patch has been picked up by major Linux distros (Red Hat, Debian, SUSE, etc), so there is a reasonable probability that you are in good shape. To test, execute this command from within a bash shell: foo='() { echo not patched; }' bash -c foo If you see "not patched", you probably want upgrade immediately. If you see "bash: foo: command not found", you're OK. == Vulnerability details: CVE-2014-6277 (the more involved one) == The following function definition appearing in the value of any environmental variable passed to bash will lead to an attempt to dereference attacker-controlled pointers (provided that the targeted instance of bash is protected only with the original patches [1][2] and does not include Florian's fix): () { x() { _; }; x() { _; } <<a; } A more complete example leading to a deref of 0x41414141 would be: HTTP_COOKIE="() { x() { _; }; x() { _; } <<`perl -e '{print "A"x1000}'`; }" bash -c : bash[25662]: segfault at 41414141 ip 00190d96 sp bfbe6354 error 4 in libc-2.12.so[110000+191000] (If you are seeing 0xdfdfdfdf, see note later on). The issue is caused by an uninitialized here_doc_eof field in a REDIR struct originally created in make_redirection(). The initial segv will happen due to an attempt to read and then copy a string to a new buffer through a macro that expands to: strcpy (xmalloc (1 + strlen (redirect->here_doc_eof)), (redirect->here_doc_eof)) This appears to be exploitable in at least one way: if here_doc_eof is chosen by the attacker to point in the vicinity of the current stack pointer, the apparent contents of the string - and therefore its length - may change between stack-based calls to xmalloc() and strcpy() as a natural consequence of an attempt to pass parameters and create local variables. Such a mid-macro switch will result in an out-of-bounds write to the newly-allocated memory. A simple conceptual illustration of this attack vector would be: -- snip! -- char* result; int len_alloced; main(int argc, char** argv) { /* The offset will be system- and compiler-specific */; char* ptr = &ptr - 9; result = strcpy (malloc(100 + (len_alloced = strlen(ptr))), ptr); printf("requested memory = %d\n" "copied text = %d\n", len_alloced + 1, strlen(result) + 1); } -- snip! -- When compiled with the -O2 flag used for bash, on one test system, this produces: requested memory = 2 copied text = 28 This can lead to heap corruption, with multiple writes possible per payload by simply increasing the number of malformed here-docs. The consequences should be fairly clear. [ There is also a latter call to free() on here_doc_eof in dispose_cmd.c, but because of the simultaneous discovery of the much simpler bug '78 discussed in the next section, I have not spent a whole lot of time trying to figure out how to get to that path. ] Perhaps notably, the ability to specify attacker-controlled addresses hinges on the state of --enable-bash-malloc and --enable-mem-scramble compile-time flags; if both are enabled, the memory returned by xmalloc() will be initialized to 0xdf, making the prospect of exploitation more speculative (essentially depending on whether the stack or any other memory region can be grown to overlap with 0xdfdfdfdf). That said, many Linux distributions disable one or both flags and are vulnerable out-of-the-box. It is also of note that relatively few distributions compile bash as PIE, so there is little consolation to be found in ASLR. Similarly to the original vulnerability, this issue can be usually triggered remotely through web servers such as Apache (provided that they invoke CGI scripts or PHP / Python / Perl / C / Java servlets that rely on system() or popen()-type libcalls); through DHCP clients; and through some MUAs and MTAs. For a more detailed discussion of the exposed attack surface, refer to [6]. == Vulnerability details: CVE-2014-6278 (the "back to the '90s" one) == The following function definition appearing in the value of any environmental variable passed to bash 4.2 or 4.3 will lead to straightforward put-your-command-here RCE (again, provided that the targeted instance is not protected with Florian's patch): () { _; } >_[$($())] { echo hi mom; id; } A complete example looks like this: HTTP_COOKIE='() { _; } >_[$($())] { echo hi mom; id; }' bash -c : ...or: GET /some/script.cgi HTTP/1.0 User-Agent: () { _; } >_[$($())] { id >/tmp/hi_mom; } Note that the PoC does not work as-is in more ancient versions of bash, such as 2.x or 3.x; it might have been introduced with xparse_dolparen() starting with bash 4.2 patch level 12 few years back, but I have not investigated this in a lot of detail. Florian's patch is strongly recommended either way. The attack surface through which this flaw may be triggered is roughly similar to that for CVE-2014-6277 and the original bash bug [6]. == Additional info == Both of these issues were identified in an automated fashion with american fuzzy lop: https://code.google.com/p/american-fuzzy-lop The out-of-the-box fuzzer was seeded with a minimal valid function definition ("() { foo() { foo; }; >bar; }") and allowed to run for a couple of hours on a single core. In addition to the issues discussed above, the fuzzer also hit three of the four previously-reported CVEs. I initially shared the findings privately with vendors, but because of the intense scrutiny that this codebase is under, the ease of reproducing these results with an open-source fuzzer, and the now-broad availability of upstream mitigations, there seems to be relatively little value in continued secrecy. == References == [1] http://ftp.gnu.org/gnu/bash/bash-4.3-patches/bash43-025 [2] http://ftp.gnu.org/gnu/bash/bash-4.3-patches/bash43-026 [3] http://www.openwall.com/lists/oss-security/2014/09/25/13 [4] http://ftp.gnu.org/gnu/bash/bash-4.3-patches/bash43-027 [5] http://lcamtuf.blogspot.com/2014/09/bash-bug-apply-unofficial-patch-now.html [6] http://lcamtuf.blogspot.com/2014/09/quick-notes-about-bash-bug-its-impact.html [7] http://www.pcworld.com/article/2688932/improved-patch-tackles-new-shellshock-attack-vectors.html PS. There are no other bugs in bash. --------- FOLLOW UP ----------- Date: Wed, 01 Oct 2014 07:32:57 -0700 From fulldisclosure-bounces@seclists.org Wed Oct 1 14:37:33 2014 From: Paul Vixie <paul@redbarn.org> To: Michal Zalewski <lcamtuf@coredump.cx> Cc: "fulldisclosure@seclists.org" <fulldisclosure@seclists.org> Subject: Re: [FD] the other bash RCEs (CVE-2014-6277 and CVE-2014-6278) michal, thank you for your incredibly informative report here. i have a minor correction. > Michal Zalewski <mailto:lcamtuf@coredump.cx> > Wednesday, October 01, 2014 7:21 AM > ... > > Note: over the past few days, Florian's patch has been picked up by > major Linux distros (Red Hat, Debian, SUSE, etc), so there is a > reasonable probability that you are in good shape. To test, execute > this command from within a bash shell: > > foo='() { echo not patched; }' bash -c foo this command need not be executed from within bash. the problem occurs when bash is run by the command, and the shell that runs the command can be anything. for example, on a system where i have deliberately not patched bash, where sh is "ash" (almquist shell): > $ foo='() { echo not patched; }' bash -c foo > not patched here's me testing it from within tcsh: > % env foo='() { echo not patched; }' bash -c foo > not patched > % (setenv foo '() { echo not patched; }'; bash -c foo) > not patched this is a minor issue, but i've found in matters of security bug reports, tests, and discussions, that any minor matter can lead to deep misunderstanding. thanks again for your excellent report, and your continuing work on this issue. vixie . This bulletin will be revised when the update is available. MITIGATION INFORMATION HP recommends the following steps to reduce the risk of this vulnerability: - Place the HP StoreFabric H-series switch and other data center critical infrastructure behind a firewall to disallow access from the Internet. - Change all HP StoreFabric switch default account passwords, including the root passwords, from the default factory passwords. - Examine the list of accounts, including ones on the switch and those existing on remote authentication servers such as RADIUS, LDAP, and TACAS+, to ensure only necessary personnel can gain access to HP StoreFabric H-series switches. Delete guest accounts and temporary accounts created for one-time usage needs. - To avoid possible exploit through the embedded web GUI, QuickTools, disable the web server with the following procedure: NOTE: After completing this procedure, the user will not be able to manage the switch using QuickTools. 1. Login to the Command Line Interface (CLI). 2. Execute the "admin start" command to enter into an admin session. 3. Execute the "set setup services" command and change setting for EmbeddedGUIEnabled to "False". HP Vertica AMI's and Virtual Machines prior to v7.1.1-0. BACKGROUND HP Vertica AMI's and Virtual Machines prior to v7.1.1-0 include a vulnerable version of the Bash shell. HP has released the following updates to resolve this vulnerability for HP Vertica products. Under Step2: your ITRC operating systems - verify your operating system selections are checked and save. To update an existing subscription: http://h30046.www3.hp.com/subSignIn.php Log in on the web page: Subscriber's choice for Business: sign-in. On the web page: Subscriber's Choice: your profile summary - use Edit Profile to update appropriate sections. HP is continually reviewing and enhancing the security features of software products to provide customers with current secure solutions. "HP is broadly distributing this Security Bulletin in order to bring to the attention of users of the affected HP products the important security information contained in this Bulletin. HP recommends that all users determine the applicability of this information to their individual situations and take appropriate action. HP does not warrant that this information is necessarily accurate or complete for all user situations and, consequently, HP will not be responsible for any damages resulting from user's use or disregard of the information provided in this Bulletin. To the extent permitted by law, HP disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose, title and non-infringement." Copyright 2014 Hewlett-Packard Development Company, L.P. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 _______________________________________________________________________ Mandriva Linux Security Advisory MDVSA-2014:186 http://www.mandriva.com/en/support/security/ _______________________________________________________________________ Package : bash Date : September 24, 2014 Affected: Business Server 1.0 _______________________________________________________________________ Problem Description: A flaw was found in the way Bash evaluated certain specially crafted environment variables. An attacker could use this flaw to override or bypass environment restrictions to execute shell commands. Certain services and applications allow remote unauthenticated attackers to provide environment variables, allowing them to exploit this issue (CVE-2014-6271). _______________________________________________________________________ References: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-6271 https://rhn.redhat.com/errata/RHSA-2014-1293.html _______________________________________________________________________ Updated Packages: Mandriva Business Server 1/X86_64: ee177bd2ef1c738689a7d04b166dc516 mbs1/x86_64/bash-4.2-6.2.mbs1.x86_64.rpm f73489d530f8c2467c4fa353bfbe61b5 mbs1/x86_64/bash-doc-4.2-6.2.mbs1.x86_64.rpm 062d5951a3a0bbbeb06fa292c8e3992b mbs1/SRPMS/bash-4.2-6.2.mbs1.src.rpm _______________________________________________________________________ To upgrade automatically use MandrivaUpdate or urpmi. The verification of md5 checksums and GPG signatures is performed automatically for you. All packages are signed by Mandriva for security. You can obtain the GPG public key of the Mandriva Security Team by executing: gpg --recv-keys --keyserver pgp.mit.edu 0x22458A98 You can view other update advisories for Mandriva Linux at: http://www.mandriva.com/en/support/security/advisories/ If you want to report vulnerabilities, please contact security_(at)_mandriva.com _______________________________________________________________________ Type Bits/KeyID Date User ID pub 1024D/22458A98 2000-07-10 Mandriva Security Team <security*mandriva.com> -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iD8DBQFUIu2fmqjQ0CJFipgRAnb/AJ4q+KC8KfRB7YxJnEJEOXCQ1d3HegCgzraD U17FsPFmznt8oJi07S3GHJQ= =mWIF -----END PGP SIGNATURE-----

AFFECTED PRODUCTS