Phishing vulnerability: Template generation allows external parameters to override placeholders

[Etienne Dysli Metref]

Upstream advisory: https://shibboleth.net/community/advisories/secadv_20210317.txt

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Shibboleth Service Provider Security Advisory [17 March 2021]

An updated version of the Service Provider software is available
which fixes a phishing vulnerability.

Template generation allows external parameters to override placeholders
======================================================================
The SP includes a primitive template engine used to render error pages
and various other status or transition pages, and it supports a syntax
for embedding placeholders that are replaced by internally supplied
values or configuration settings.

For reasons that are unclear in the code history, it was extended to
allow replacement via query parameters also, though this is not a
typical need. Because of this feature, it's possible to cause the SP
to display some templates containing values supplied externally by
URL manipulation.

Though the values are encoded to prevent script injection, the content
nevertheless appears to come from the server and so would be interpreted
as trustworthy, allowing email addresses, logos and style sheets, or
support URLs to be manipulated by an attacker.

All platforms are impacted by this issue.

Recommendations
===============
Update to V3.2.1 or later of the Service Provider software, which
is now available.

The update adds a new <Errors> setting to the configuration called
externalParameters, which defaults to false. When false, support for
this "feature" is disabled. In the unlikely event that a valid need
for this exists, the setting can be enabled temporarily to maintain
function until the use case requiring it is addressed in some other
way.

In the event that an update is not possible, reducing or eliminating
some of the more sensitive template replacement values with static
values in the templates may decrease the impact.

Other Notes
===========
The cpp-sp git commit containing the fix for this issue is
d1dbebfadc1bdb824fea63843c4c38fa69e54379

Credits
=======
Toni Huttunen, Fraktal Oy

History
=======
Edited to add credit, and a bit more discussion of style sheet risk
and workarounds.

URL for this Security Advisory:
https://shibboleth.net/community/advisories/secadv_20210317.txt

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Upstream bug: https://issues.shibboleth.net/jira/browse/SSPCPP-922
Upstream patch: https://git.shibboleth.net/view/?p=cpp-sp.git;a=commit;h=d1dbebfadc1bdb824fea63843c4c38fa69e54379

[Etienne Dysli Metref (etienne-dysli-metref)]

Patch for focal copied from Debian buster's 3.0.4 security fix.

[Etienne Dysli Metref (etienne-dysli-metref)]

Assigned CVE: 2021-28963
https://security-tracker.debian.org/tracker/CVE-2021-28963

For some reason, the "link to CVE" on the right rejects "2021-28963"...

[Etienne Dysli Metref (etienne-dysli-metref)]

Is there something missing from the proposed patch?

[Steve Beattie (sbeattie)]

Hey Etienne,

Thanks for submitting the debdiff. I'm taking a look in more detail, but on first glance it looks good to me. If all goes well, I'll push it up to our security-proposed in a bit.

[Steve Beattie (sbeattie)]

I have pushed the focal update to the security-proposed ppa at https://launchpad.net/~ubuntu-security-proposed/+archive/ubuntu/ppa/+packages ; any testing that anyone could give once it is done building would be appreciated.

Thanks!

[Launchpad Janitor (janitor)]

This bug was fixed in the package shibboleth-sp - 3.0.4+dfsg1-1ubuntu0.1

---------------
shibboleth-sp (3.0.4+dfsg1-1ubuntu0.1) focal-security; urgency=high

  * SECURITY UPDATE: Fix a phishing vulnerability: Template generation
    allows external parameters to override placeholders (LP: #1919419)
    - debian/patches/SSPCPP-922-Add-externalParameters-option-to-Errors-
      element.patch: Add externalParameters option to Errors element
    - https://shibboleth.net/community/advisories/secadv_20210317.txt
    - https://issues.shibboleth.net/jira/browse/SSPCPP-922
    - CVE-2021-28963

 -- Etienne Dysli Metref <email address hidden> Thu, 18 Mar 2021 12:22:53 +0100