Home    |    View Topics    |    Search    |    Contact Us    |   



Category:   Application (Web Server/CGI)  >   Squid Vendors:
Squid SSL-Bump Certificate Validation Flaw Lets Remote Servers Bypass Client-side Certificate Validation
SecurityTracker Alert ID:  1032221
SecurityTracker URL:
CVE Reference:   CVE-2015-3455   (Links to External Site)
Date:  May 1 2015
Impact:   Modification of authentication information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 3.2 - 3.2.13, 3.3 - 3.3.13, 3.4 - 3.4.12, 3.5 - 3.5.3
Description:   A vulnerability was reported in Squid. A remote user can bypass security controls on the target system.

The client-first SSL-bump feature does not properly validate X.509 server certificate domain and hostname fields. A remote server can create a specially crafted certificate to bypass client certificate validation.

Only systems configured to perform SSL Bumping with the "client-first" or "bump" mode of operations are affected.

Impact:   A remote server can bypass client certificate validation.
Solution:   The vendor has issued a fix (3.2.14, 3.3.14, 3.4.13, 3.5.4).

The vendor's advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Authentication error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Nov 20 2015 (Red Hat Issues Fix) Squid SSL-Bump Certificate Validation Flaw Lets Remote Servers Bypass Client-side Certificate Validation
Red Hat has issued a fix for Red Hat Enterprise Linux 7.

 Source Message Contents

Subject:  [oss-security] CVE-2015-3455 - SQUID-2015:1 Incorrect X509 server certificate validation

Hash: SHA1


    Squid Proxy Cache Security Update Advisory SQUID-2015:1

Advisory ID:            SQUID-2015:1
Date:                   May 01, 2015
Summary:                Incorrect X509 server certificate validation
Affected versions:      Squid 3.2 -> 3.2.13
                        Squid 3.3 -> 3.3.13
                        Squid 3.4 -> 3.4.12
                        Squid 3.5 -> 3.5.3
Fixed in version:       Squid 3.5.4, 3.4.13, 3.3.14, 3.2.14

Problem Description:

 Squid configured with client-first SSL-bump does not correctly
 validate X509 server certificate domain / hostname fields.



 The bug is important because it allows remote servers to bypass
 client certificate validation. Some attackers may also be able
 to use valid certificates for one domain signed by a global
 Certificate Authority to abuse an unrelated domain.

 However, the bug is exploitable only if you have configured
 Squid to perform SSL Bumping with the "client-first" or "bump"
 mode of operation.

 Sites that do not use SSL-Bump are not vulnerable.


Updated Packages:

 This bug is fixed by Squid version 3.5.4, 3.4.13, 3.3.14, and

 In addition, patches addressing this problem for stable releases
 can be found in our patch archives:

Squid 3.2:

Squid 3.3:

Squid 3.4:

Squid 3.5:

 If you are using a prepackaged version of Squid then please refer
 to the package vendor for availability information on updated


Determining if your version is vulnerable:

 All Squid-2.x, 3.0 and 3.1 are not vulnerable to the problem.

1) Run "squid -v" to determine if SSL support is enabled.

 All Squid built without SSL support are not vulnerable to the

2) Run "squid -k parse 2>&1 | grep ssl_bump" to determine if
SSL-Bump is being used.

 All Squid-3.2, 3.3, 3.4, and 3.5 operating with ssl_bump omitted
 from squid.conf are not vulnerable to the problem.

 All unpatched Squid-3.x operating with "ssl_bump client-first"
 in squid.conf are vulnerable to the problem.

 All unpatched Squid-3.x operating with "ssl_bump bump" in
 squid.conf are vulnerable to the problem.



 There is no workaround for Squid-3.2.

 For Squid-3.3 and 3.4, upgrade the squid.conf settings to use
 "ssl_bump server-first".

 For Squid-3.5, upgrade the squid.conf settings to use a
 "ssl_bump peek" operation before the "bump" operation.

  NOTE that these workarounds do not resolve the vulnerability,
  but allow Squid to relay (or mimic) the invalid certificate to
  clients and depends on validation in the client.


 Disable SSL-Bump. Which may be done in the following ways:

 * Build Squid-3.2, 3.3, or 3.4 with ./configure --disable-ssl

 * Build Squid-3.5 with ./configure --without-openssl

 * Remove from squid.conf (and include'd files) any ssl_bump


Contact details for the Squid project:

 For installation / upgrade support on binary packaged versions
 of Squid: Your first point of contact should be your binary
 package vendor.

 If you install and build Squid from the original Squid sources
 then the mailing list is your primary
 support point. For subscription details see

 For reporting of non-security bugs in the latest release
 the squid bugzilla database should be used

 For reporting of security sensitive bugs send an email to the mailing list. It's a closed list
 (though anyone can post) and security related bug reports are
 treated in confidence until the impact has been established.



 The vulnerability was discovered and reported by a contributor
 who wishes to remain anonymous.

 The vulnerability was fixed and tested by
  Amos Jeffries, Treehouse Networks Ltd. and
  Christos Tsantilas, The Measurement Factory.


Revision history:

 2015-04-29 01:35 GMT Initial Report
 2015-05-01 13:49 GMT CVE Assignment
 2015-05-01 12:50 GMT Patches and Packages Released
Version: GnuPG v2.0.22 (MingW32)


Go to the Top of This SecurityTracker Archive Page

Home   |    View Topics   |    Search   |    Contact Us

This web site uses cookies for web analytics. Learn More

Copyright 2019, LLC