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CERT Coordination Center


Proxy auto-config (PAC) files have access to full HTTPS URLs

Vulnerability Note VU#877625

Original Release Date: 2016-08-04 | Last Revised: 2017-07-11

Overview

Web proxy auto-config (PAC) files are passed the full HTTPS URL in GET requests which may expose sensitive data.

Description

CWE-212: Improper Cross-boundary Removal of Sensitive Data - CVE-2016-5134 (Google), CVE-2016-1801 (Apple)

Web proxy auto-configuration files (proxy.pac) have access to the full URL including the path and parameters in HTTPS GET requests, which may expose sensitive data intended to be protected by HTTPS. This information is passed to the FindProxyForURL() function in the proxy.pac. The PAC file is often retrieved by the browser automatically using the WPAD protocol. An attacker in the position to conduct man-in-the-middle attacks may provide a malicious PAC file capable of exploiting the FindProxyForURL() function to exfiltrate sensitive data.

Impact

An attacker who can provide a specially crafted PAC file can read URLs, including the path and query string, which may contain sensitive information intended to be protected by HTTPS.

Solution

Apply an update.

Apply the latest updates to your browser, see Vendor Information section below.

Users who are unable to or do not wish to update their browsers should consider the following workaround.

Disable WPAD.

If proxy auto-configuration is not necessary, consider disabling WPAD functionality for your browser.

Vendor Information

This vendors listed below are suspected to be affected by the vulnerability. Other browser vendors not listed may be affected as well. The CERT/CC has no further evidence that any particular vendor is impacted unless marked Affected; vendors are encouraged to reach out to us to clarify their status.

877625
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Apple

Notified:  July 27, 2016 Updated:  August 04, 2016

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Addendum

There are no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Google

Notified:  July 27, 2016 Updated:  August 04, 2016

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Addendum

There are no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Mozilla

Notified:  July 27, 2016 Updated:  August 04, 2016

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Addendum

There are no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Opera

Notified:  July 27, 2016 Updated:  August 04, 2016

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Addendum

There are no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Microsoft Corporation

Notified:  July 27, 2016 Updated:  July 11, 2017

Statement Date:   August 17, 2016

Status

  Not Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Addendum

Microsoft has informed CERT/CC that they are unaffected.

If you have feedback, comments, or additional information about this vulnerability, please send us email.


CVSS Metrics

Group Score Vector
Base 2.9 AV:A/AC:M/Au:N/C:P/I:N/A:N
Temporal 2.3 E:POC/RL:OF/RC:C
Environmental 1.7 CDP:ND/TD:M/CR:ND/IR:ND/AR:ND

References

Credit

Thanks to Bas Venis for reporting this vulnerability. We also would like to thank Itzik Kotler and Amit Klein for their presentation at Black Hat 2016, and Alex Chapman and Paul Stone for their presentation at DEF CON 24

This document was written by Trent Novelly.

Other Information

CVE IDs: CVE-2016-5134, CVE-2016-1801
Date Public: 2016-08-04
Date First Published: 2016-08-04
Date Last Updated: 2017-07-11 19:46 UTC
Document Revision: 24

Sponsored by the Department of Homeland Security Office of Cybersecurity and Communications.