ID

VAR-201409-0366

CVE

CVE-2014-6277

TITLE

GNU Bash shell executes commands in exported functions in environment variables

DESCRIPTION

GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized memory access, and untrusted-pointer read and write operations) 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. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-6271 and CVE-2014-7169. 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. This vulnerability allows users that have been granted access to a shell script to escalate privilege and execute unrestricted commands at the same security level as the Bash script. Customers who need to upgrade the firmware of their Superdome X or HP Converged System 900 for SAP HANA should contact HP Technical Support to obtain the firmware or plan to schedule an onsite visit with an HP Services field service professional. Patch and maintain Lightweight Directory Access Protocol (LDAP) and web servers. Use virus scanners, intrusion detection/prevention systems (IDS/IPS), and vulnerability scanners regularly. Apply all recommended HP Firmware updates. ============================================================================ Ubuntu Security Notice USN-2380-1 October 09, 2014 bash vulnerabilities ============================================================================ A security issue affects these releases of Ubuntu and its derivatives: - Ubuntu 14.04 LTS - Ubuntu 12.04 LTS - Ubuntu 10.04 LTS Summary: Several security issues were fixed in Bash. If an attacker were able to create an environment variable containing a function definition with a very specific name, these issues could possibly be used to bypass certain environment restrictions and execute arbitrary code. (CVE-2014-6277, CVE-2014-6278) Please note that the previous Bash security update, USN-2364-1, includes a hardening measure that prevents these issues from being used in a Shellshock attack. Update instructions: The problem can be corrected by updating your system to the following package versions: Ubuntu 14.04 LTS: bash 4.3-7ubuntu1.5 Ubuntu 12.04 LTS: bash 4.2-2ubuntu2.6 Ubuntu 10.04 LTS: bash 4.1-2ubuntu3.5 In general, a standard system update will make all the necessary changes. References: http://www.ubuntu.com/usn/usn-2380-1 CVE-2014-6277, CVE-2014-6278 Package Information: https://launchpad.net/ubuntu/+source/bash/4.3-7ubuntu1.5 https://launchpad.net/ubuntu/+source/bash/4.2-2ubuntu2.6 https://launchpad.net/ubuntu/+source/bash/4.1-2ubuntu3.5 . 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 . No other firmware stream updates are planned beyond the NX-OS 5.x and 6.x versions listed below for the MDS products. HP has released and posted the Cisco switch software version NX-OS 6.2(9a) on HP Support Center (HPSC). This software versions 6.2(9a) has included the fixes for the vulnerability in HP StoreFabric C-series MDS switches which currently supporting NX-OS 6.X releases. HP has released and posted the Cisco switch software version NX-OS 5.2(8e) on HP Support Center (HPSC). This software version 5.2(8e) has included the fix for the vulnerability in HP C-series MDS switches which currently supporting NX-OS 5.X releases. All MDS and Nexus 5K switches can function in this configuration. Access is available through the console port. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Gentoo Linux Security Advisory GLSA 201410-01 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - http://security.gentoo.org/ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Severity: High Title: Bash: Multiple vulnerabilities Date: October 04, 2014 Bugs: #523742, #524256 ID: 201410-01 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Synopsis ======== Multiple parsing flaws in Bash could allow remote attackers to inject code or cause a Denial of Service condition. Background ========== Bash is the standard GNU Bourne Again SHell. Affected packages ================= ------------------------------------------------------------------- Package / Vulnerable / Unaffected ------------------------------------------------------------------- 1 app-shells/bash < 4.2_p52 *>= 3.1_p22 *>= 3.2_p56 *>= 4.0_p43 *>= 4.1_p16 >= 4.2_p52 Description =========== Florian Weimer, Todd Sabin, Michal Zalewski et al. discovered further parsing flaws in Bash. The unaffected Gentoo packages listed in this GLSA contain the official patches to fix the issues tracked as CVE-2014-6277, CVE-2014-7186, and CVE-2014-7187. Workaround ========== There is no known workaround at this time. Resolution ========== All Bash 3.1 users should upgrade to the latest version: # emerge --sync # emerge --ask --oneshot --verbose ">=app-shells/bash-3.1_p22:3.1" All Bash 3.2 users should upgrade to the latest version: # emerge --sync # emerge --ask --oneshot --verbose ">=app-shells/bash-3.2_p56:3.2" All Bash 4.0 users should upgrade to the latest version: # emerge --sync # emerge --ask --oneshot --verbose ">=app-shells/bash-4.0_p43:4.0" All Bash 4.1 users should upgrade to the latest version: # emerge --sync # emerge --ask --oneshot --verbose ">=app-shells/bash-4.1_p16:4.1" All Bash 4.2 users should upgrade to the latest version: # emerge --sync # emerge --ask --oneshot --verbose ">=app-shells/bash-4.2_p52" References ========== [ 1 ] CVE-2014-6277 http://nvd.nist.gov/nvd.cfm?cvename=CVE-2014-6277 [ 2 ] CVE-2014-6278 http://nvd.nist.gov/nvd.cfm?cvename=CVE-2014-6278 [ 3 ] CVE-2014-7186 http://nvd.nist.gov/nvd.cfm?cvename=CVE-2014-7186 [ 4 ] CVE-2014-7187 http://nvd.nist.gov/nvd.cfm?cvename=CVE-2014-7187 Availability ============ This GLSA and any updates to it are available for viewing at the Gentoo Security Website: http://security.gentoo.org/glsa/glsa-201410-01.xml Concerns? ========= Security is a primary focus of Gentoo Linux and ensuring the confidentiality and security of our users' machines is of utmost importance to us. Any security concerns should be addressed to security@gentoo.org or alternatively, you may file a bug at https://bugs.gentoo.org. License ======= Copyright 2014 Gentoo Foundation, Inc; referenced text belongs to its owner(s). The contents of this document are licensed under the Creative Commons - Attribution / Share Alike license. http://creativecommons.org/licenses/by-sa/2.5 . -----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-c04487573 SUPPORT COMMUNICATION - SECURITY BULLETIN Document ID: c04487573 Version: 1 HPSBST03155 rev.1 - HP StoreFabric H-series switches running Bash Shell, Remote Code Execution NOTICE: The information in this Security Bulletin should be acted upon as soon as possible. Release Date: 2014-11-11 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 StoreFabric H-series switches running Bash Shell. References: CVE-2014-6271 CVE-2014-6277 CVE-2014-6278 CVE-2014-7169 CVE-2014-7186 CVE-2014-7187 SSRT101747 SUPPORTED SOFTWARE VERSIONS*: ONLY impacted versions are listed. All HP StoreFabric H-series switches 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-2014-6277 (AV:N/AC:L/Au:N/C:C/I:C/A:C) 10.0 CVE-2014-6278 (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 CVE-2014-7186 (AV:N/AC:L/Au:N/C:C/I:C/A:C) 10.0 CVE-2014-7187 (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 is actively working on a firmware update to resolve the vulnerability in HP StoreFabric H-series switches. 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". HISTORY Version:1 (rev.1) - 11 November 2014 Initial release 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) iEYEARECAAYFAlRih1AACgkQ4B86/C0qfVkTcACgxGfOP4MElysfECAvNJSqkgk2 LCAAn0YGgpGgh493pj4rgB8hPH0PETxo =X8Sm -----END PGP SIGNATURE----- . Note: HP and the switch vendor recommend running an active version of Fabric OS (FOS) listed on the HP Single Point of Connectivity Knowledge (SPOCK) website ( http://h20272.www2.hp.com/ ) and applying the work-around information provided in the MITIGATION INFORMATION section below to protect HP StoreFabric B-series switches from this vulnerability. - Utilize FOS password policy management to strengthen the complexity, age, and history requirements of switch account passwords

AFFECTED PRODUCTS

CVSS

PROBLEMTYPE DATA

THREAT TYPE

remote

TYPE

operating system commend injection

EXPLOIT AVAILABILITY

PATCH

EXTERNAL IDS

REFERENCES

CREDITS

HP

SOURCES

LAST UPDATE DATE

2025-11-20T22:30:53.147000+00:00

SOURCES UPDATE DATE

SOURCES RELEASE DATE