[Bug 1698758] [NEW] Encrypted password causes segmentation fault

Wed Jul 19 21:22:04 UTC 2017

You have been subscribed to a public bug by Andreas Hasenack (ahasenack):

[Impact]
The libapache2-mod-auth-pgsql module will cause a segfault error in apache if its encrypted support is enabled ("Auth_PG_encrypted on") and a hash format not supported by crypt(3) is used.

Since this is an apache module, users might be tempted to use
htpasswd(1) to generate such hashes. The option to generate SHA hashes
(-s) in particular will generate a hash incompatible with crypt(3),
which will then return NULL and cause the segfault in unpatched versions
of this apache module.

The fix catches the situation when crypt(3) returns NULL and logs the
event as an unsupported hash type being found, and denies the login.

[Test Case]

* install the packages on the Ubuntu release you are testing:
$ sudo apt install apache2 libapache2-mod-auth-pgsql postgresql

* create the database and populate it with the test users from the attached test-users.sql file:
$ sudo -u postgres -H createdb userdb
$ sudo -u postgres -H psql userdb -f test-users.sql

* Create the DB user we will use:
$ sudo -u postgres -H psql postgres -c "CREATE ROLE www UNENCRYPTED PASSWORD 'password' NOSUPERUSER NOCREATEDB NOCREATEROLE INHERIT LOGIN;"

* Grant access:
$ sudo -u postgres -H psql userdb -c "GRANT SELECT ON TABLE userlogin TO www;"

* Create the /var/www/html/.htaccess file with this content:
AuthType basic
AuthName "My Auth"
Require valid-user
AuthBasicProvider pgsql
Auth_PG_authoritative On
Auth_PG_host 127.0.0.1
Auth_PG_port 5432
Auth_PG_user www
Auth_PG_pwd password
Auth_PG_database userdb
Auth_PG_encrypted on
Auth_PG_pwd_table UserLogin
Auth_PG_uid_field Username
Auth_PG_pwd_field ApachePassword

* Setup access in apache by editing /etc/apache2/sites-
enabled/000-default.conf and adding these lines somewhere inside the
<virtualhost> section:

<Directory /var/www/html>
    AllowOverride AuthConfig
</Directory>

* Enable the mod-auth-pgsql module:
$ sudo a2enmod 000_auth_pgsql

* Restart apache:
$ sudo service apache2 restart

To try each test login, use a loop like this:

$ for u in ubuntu-invalidhash ubuntu-md5 ubuntu-sha256 ubuntu-sha512 ubuntu-des; do echo -n "Testing $u... "; curl -f http://$u:secret@localhost/ -o /dev/null -s; echo $?; done
Testing ubuntu-invalidhash... 52
Testing ubuntu-md5... 0
Testing ubuntu-sha256... 0
Testing ubuntu-sha512... 0
Testing ubuntu-des... 0

Error 52 means "empty reply from server". That's when apache segfaulted:
[Wed Jul 19 19:28:13.808711 2017] [core:notice] [pid 9499:tid 140330145511296] AH00051: child pid 9677 exit signal Segmentation fault (11), possible coredump in /etc/apache2

With the fixed version of libapache2-mod-auth-pgsql, the test loop will
just record a normal authentication problem for the ubuntu-invalidhash
user (since the hash is not supported) instead of an "empty reply from
server":

$ for u in ubuntu-invalidhash ubuntu-md5 ubuntu-sha256 ubuntu-sha512 ubuntu-des; do echo -n "Testing $u... "; curl -f http://$u:secret@localhost/ -o /dev/null -s; echo $?; done
Testing ubuntu-invalidhash... 22
Testing ubuntu-md5... 0
Testing ubuntu-sha256... 0
Testing ubuntu-sha512... 0
Testing ubuntu-des... 0

And we get this fact logged:
[Wed Jul 19 19:38:56.547337 2017] [auth_pgsql:error] [pid 10035:tid 140550732678912] [client 127.0.0.1:56946] [mod_auth_pgsql.c] - ERROR - PG user ubuntu-invalidhash: unsupported CRYPT format

[Regression Potential]
The patch seems pretty straight forward and uses a well documented crypt(3) return value in the case of errors.

This is a very old module that hasn't been built in a while (see [other
info] below. It's possible that just by rebuilding it with the new
environment available in each ubuntu release since vivid could introduce
unknowns. Hopefully, if that happens, it will be immediately noticed by
the people who use it and will test this SRU.

[Other Info]

Upstream doesn't have a bugtracker or public code hosting that I could
find, so I forwarded the patch via email. No response so far.

This module hasn't been rebuilt since vivid and seems unmaintained, being at version 2.0.3 since the precise days:
 libapache2-mod-auth-pgsql | 2.0.3-5build2    | precise
 libapache2-mod-auth-pgsql | 2.0.3-6          | trusty
 libapache2-mod-auth-pgsql | 2.0.3-6.1        | vivid
 libapache2-mod-auth-pgsql | 2.0.3-6.1        | xenial
 libapache2-mod-auth-pgsql | 2.0.3-6.1        | yakkety
 libapache2-mod-auth-pgsql | 2.0.3-6.1        | zesty
 libapache2-mod-auth-pgsql | 2.0.3-6.1ubuntu1 | artful

- Debian's last changelog entry is from August 2013
- Fedora killed it in July 2011
- I couldn't find it in SuSE

** Affects: libapache2-mod-auth-pgsql (Ubuntu)
     Importance: High
     Assignee: Andreas Hasenack (ahasenack)
         Status: Fix Released

** Affects: libapache2-mod-auth-pgsql (Ubuntu Trusty)
     Importance: High
     Assignee: Andreas Hasenack (ahasenack)
         Status: In Progress

** Affects: libapache2-mod-auth-pgsql (Ubuntu Xenial)
     Importance: High
     Assignee: Andreas Hasenack (ahasenack)
         Status: In Progress

** Affects: libapache2-mod-auth-pgsql (Ubuntu Zesty)
     Importance: High
     Assignee: Andreas Hasenack (ahasenack)
         Status: In Progress

** Affects: libapache2-mod-auth-pgsql (Debian)
     Importance: Unknown
         Status: New

** Tags: amd64 server-next xenial
-- 
Encrypted password causes segmentation fault
https://bugs.launchpad.net/bugs/1698758
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