cups is intolerant to TLS 1.2

[Laine Gholson]

CUPS 1.7.2-0ubuntu1.7 on Ubuntu Trusty has a security problem where connections using TLS 1.2 will fail, forcing a TLS 1.1 retry

=== How to reproduce ====
1. Connect to the cups server with HTTPS
2. Check the security info

or

1. openssl s_client -connect localhost:631
2. See the error
3. openssl s_client -tls1_1 -connect localhost:631
4. See no error

TLS 1.1 is not the newest protocol version, and therefore this can be considered a security issue.

[Marc Deslauriers (mdeslaur)]

Curiously, I can't reproduce that. This is what I get:

$ openssl s_client -connect localhost:631
<snip>
SSL-Session:
    Protocol : TLSv1.2
    Cipher : AES256-SHA256
<snip>

Please attach the output of "apt-cache policy libssl1.0.0" and your /etc/cups/cupsd.conf

Thanks!

[Laine Gholson (laine-gholson-deactivatedaccount)]

My cupsd.conf is:
#
#
# Sample configuration file for the CUPS scheduler. See "man cupsd.conf" for a
# complete description of this file.
#

# Log general information in error_log - change "warn" to "debug"
# for troubleshooting...
LogLevel notice

# Deactivate CUPS' internal logrotating, as we provide a better one, especially
# LogLevel debug2 gets usable now
MaxLogSize 0

# Only listen for connections from the local machine.
Listen localhost:631
Listen /var/run/cups/cups.sock

# Show shared printers on the local network.
Browsing Off
BrowseLocalProtocols dnssd

# Default authentication type, when authentication is required...
DefaultAuthType Basic

# Default encryption setting...
DefaultEncryption Required

# Web interface setting...
WebInterface Yes

# Restrict access to the server...
<Location />
# AuthType Default
# Require user @SYSTEM
  Encryption Required
  Order allow,deny
  Allow @LOCAL
</Location>

# Restrict access to the admin pages...
<Location /admin>
  AuthType Default
  Require user @SYSTEM
  Encryption Required
  Order allow,deny
  Allow @LOCAL
</Location>

# Restrict access to configuration files...
<Location /admin/conf>
  AuthType Default
  Require user @SYSTEM
  Encryption Required
  Order allow,deny
  Allow @LOCAL
</Location>

# Set the default printer/job policies...
<Policy default>
  # Job/subscription privacy...
  JobPrivateAccess default
  JobPrivateValues default
  SubscriptionPrivateAccess default
  SubscriptionPrivateValues default

  # Job-related operations must be done by the owner or an administrator...
  <Limit Create-Job Print-Job Print-URI Validate-Job>
    Order deny,allow
  </Limit>

  <Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document>
    Require user @OWNER @SYSTEM
    Order deny,allow
  </Limit>

  # All administration operations require an administrator to authenticate...
  <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default CUPS-Get-Devices>
    AuthType Default
    Require user @SYSTEM
    Order deny,allow
  </Limit>

  # All printer operations require a printer operator to authenticate...
  <Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs>
    AuthType Default
    Require user @SYSTEM
    Order deny,allow
  </Limit>

  # Only the owner or an administrator can cancel or authenticate a job...
  <Limit Cancel-Job CUPS-Authenticate-Job>
    Require user @OWNER @SYSTEM
    Order deny,allow
  </Limit>

  <Limit All>
    Order deny,allow
  </Limit>
</Policy>

# Set the authenticated printer/job policies...
<Policy authenticated>
  # Job/subscription privacy...
  JobPrivateAccess default
  JobPrivateValues default
  SubscriptionPrivateAccess default
  SubscriptionP...

[Laine Gholson (laine-gholson-deactivatedaccount)]

It's my OpenSSL, isn't it, because I am running a custom OpenSSL 1.0.2e with ChaCha20 support:
libssl1.0.0:
  Installed: 1.0.2e-0laine1
  Candidate: 1.0.2e-0laine1
  Version table:
 *** 1.0.2e-0laine1 0
        100 /var/lib/dpkg/status
     1.0.1f-1ubuntu2.16 0
        500 http://ports.ubuntu.com/ubuntu-ports/ trusty-security/main armhf Packages
        500 http://ports.ubuntu.com/ubuntu-ports/ trusty-updates/main armhf Packages
     1.0.1f-1ubuntu2 0
        500 http://ports.ubuntu.com/ubuntu-ports/ trusty/main armhf Packages

[Laine Gholson (laine-gholson-deactivatedaccount)]

Aha! I think it is that for some weird reason, a SHA-384 certificate may be the cause of this problem. I changed my server certificate to SHA-1 and TLS 1.2 works again. (and CUPS uses GnuTLS, so my OpenSSL cannot be the problem)

[Marc Deslauriers (mdeslaur)]

Since you managed to get this to work, I am closing this bug. Thanks!