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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2016.1764 CGI web servers assign Proxy header values from client requests to internal HTTP_PROXY environment variables 19 July 2016 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Web Server products running CGI Publisher: US-CERT Operating System: UNIX variants (UNIX, Linux, OSX) Windows Impact/Access: Provide Misleading Information -- Remote/Unauthenticated Unauthorised Access -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2016-1000110 CVE-2016-1000109 CVE-2016-5388 CVE-2016-5387 CVE-2016-5386 CVE-2016-5385 Original Bulletin: https://www.kb.cert.org/vuls/id/797896 Comment: Where applicable, patches should be applied to correct this issue. Where patches have not yet been released, mitigations have been provided in this bulletin for a number of products. For products where mitigations have not yet been provided, contact the product vendor for more information. - --------------------------BEGIN INCLUDED TEXT-------------------- Vulnerability Note VU#797896 CGI web servers assign Proxy header values from client requests to internal HTTP_PROXY environment variables Original Release date: 18 Jul 2016 | Last revised: 18 Jul 2016 Overview Web servers running in a CGI or CGI-like context may assign client request Proxy header values to internal HTTP_PROXY environment variables. This vulnerability can be leveraged to conduct man-in-the-middle (MITM) attacks on internal subrequests or to direct the server to initiate connections to arbitrary hosts. Description CWE-807: Reliance on Untrusted Inputs in a Security Decision, CWE-454: External Initialization of Trusted Variables or Data Stores Web servers running in a CGI or CGI-like context may assign client request Proxy header values to internal HTTP_PROXY environment variables. The vulnerable behavior is the result of a naming convention for meta-variables, defined in RFC 3876, which leads to a name collision: "The HTTP header field name is converted to upper case, has all occurrences of "-" replaced with "_" and has "HTTP_" prepended to give the meta-variable name." According to the researchers, a web server is vulnerable if: 1. A web server, programming language or framework (and in some limited situations the application itself) sets the environmental variable HTTP_PROXY from the user supplied Proxy header in the web request, or sets a similarly used variable (essentially when the request header turns from harmless data into a potentially harmful environmental variable). 2. A web application makes use of HTTP_PROXY or similar variable unsafely (e.g. fails to check the request type) resulting in an attacker controlled proxy being used (essentially when HTTP_PROXY is actually used unsafely). By sending a specially crafted request to a vulnerable server, a remote, unauthenticated attacker may be able to conduct MITM attacks on internal server subrequests or direct the server to initiate connections to arbitrary hosts. For more information, refer to httpoxy.org. Impact A remote, unauthenticated attacker may be able to conduct MITM attacks on internal server subrequests or direct the server to initiate connections to arbitrary hosts. Solution Apply an update Where applicable, affected products and components should be updated to address this vulnerability. Check with vendors for information about patching. Where patches are unavailable or updating is not an option, consider the following workarounds. Filter Proxy request headers The researchers and community have identified several filtering strategies that are product-dependent: Apache/CGI In this configuration, any language may be vulnerable (the HTTP_PROXY env var is "real"). If you are using mod_headers , you can unset the "Proxy" header with this directive: RequestHeader unset Proxy If you are using mod_security, you can use a rule like (vary the action to taste): SecRuleEngine On SecRule &REQUEST_HEADERS:Proxy "@gt 0" "id:1000005,log,deny,msg:'httpoxy denied'" Refer to Apache's response for more information. HAProxy httprequest delheader Proxy Nginx/FastCGI Use this to block the Proxy header from being passed on to PHPFPM, PHPPM, etc. fastcgi_param HTTP_PROXY ""; Nginx with proxy_pass The following setting should work for people who are using "proxy_pass" with nginx: proxy_set_header Proxy ""; Microsoft has provided the following guidance for IIS servers utilizing affected third-party frameworks: Mitigation steps: Update apphost.config with the following rule: <system.webServer> <rewrite> <rules> <rule name=3D"Erase HTTP_PROXY" patternSyntax=3D"Wildcard"> <match url=3D"*.*" /> <serverVariables> <set name=3D"HTTP_PROXY" value=3D"" /> </serverVariables> <action type=3D"None" /> </rule> </rules> </rewrite> </system.webServer> Vendor Information (Learn More) Vendor Status Date Notified Date Updated Apache HTTP Server Project Affected 12 Jul 2016 18 Jul 2016 Go Programming Language Affected - 18 Jul 2016 HAProxy Affected - 13 Jul 2016 HHVM Affected - 18 Jul 2016 Microsoft Corporation Affected 12 Jul 2016 13 Jul 2016 nginx Affected - 13 Jul 2016 Python Affected - 18 Jul 2016 The PHP Group Affected - 18 Jul 2016 EfficientIP SAS Not Affected 12 Jul 2016 12 Jul 2016 ACCESS Unknown 12 Jul 2016 12 Jul 2016 Alcatel-Lucent Unknown 12 Jul 2016 12 Jul 2016 Apple Unknown 12 Jul 2016 12 Jul 2016 Arista Networks, Inc. Unknown 12 Jul 2016 12 Jul 2016 ARRIS Unknown 12 Jul 2016 12 Jul 2016 Aruba Networks Unknown 12 Jul 2016 12 Jul 2016 If you are a vendor and your product is affected, let us know. CVSS Metrics (Learn More) Group Score Vector Base 5.1 AV:N/AC:H/Au:N/C:P/I:P/A:P Temporal 4.6 E:POC/RL:ND/RC:C Environmental 1.1 CDP:ND/TD:L/CR:ND/IR:ND/AR:ND References https://tools.ietf.org/html/rfc3875 https://httpoxy.org https://www.apache.org/security/asf-httpoxy-response.txt https://cwe.mitre.org/data/definitions/807.html https://cwe.mitre.org/data/definitions/454.html Credit Thanks to Dominic Scheirlinck and Scott Geary of Vend for reporting this vulnerability. This document was written by Joel Land. Other Information CVE IDs: CVE-2016-5385 CVE-2016-5386 CVE-2016-5387 CVE-2016-5388 CVE-2016-1000109 CVE-2016-1000110 Date Public: 18 Jul 2016 Date First Published: 18 Jul 2016 Date Last Updated: 18 Jul 2016 Document Revision: 59 Feedback If you have feedback, comments, or additional information about this vulnerability, please send us email. - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. 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On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBV41zQYx+lLeg9Ub1AQh0FhAAkKwETMxCJWfhQbiPf9g7J+IeAjwGfyQg lKwba1O8DjcsUAB13gEFDAa1vUr/95whoQDhKI5Hj2FdnO9ZIeY7ur1w5NxfRsY+ VrN2cH1Bo8SFnFqfaELJxvGEyt8eIYdFcmdLeL7GDGOlaJ/aGOJcLYcgf6EQXpmn c8mYj2+pHBcTIYpuNOVx0FNlSssP/1BrfxNJ+aWopOQUbALlkAx5gBkVfMUvn/QV mu/D9zx/86Rqm95M4LmBsT55cEb5TB26wcCHre3wE0SBErueablu3YHNsy29J1J5 u6DCIfsdhWvnsZZXvjqs63DsEmrI7XfQwVnZmNPtt1agdRNDA9aFn5uYU3lOWfke xXdjSPyvm7wG6ND/MuJTCB8rps7mgXw/hW2GUkose3tAVVMHnqCi122PfNOpJ0P3 XeOos9aHrmPfZDWJLgmuuA4zaotuQUXwRlPHkOCR48ibEKZusWTeEXpyX4AXIXzb 9Htme80TQFXzHiN4he8YdSwrh2DDW1gpPyrXY6dB5s0F6MqfOmmOr54dUpqLYLTn 6JhvshylVeerGBF1Hp7ONXvzfhpp+cmaMKlTf/ltekqd3HSVTMcR+oKyoLYgQqvv 0dGL0NKIb2SyJn95Yps7AVr9vhjgPb964imzidG943Bj39d6T62ZzotRheg5pBMu bicpdqSyVro= =BFbj -----END PGP SIGNATURE-----