2020-002 Security flaws in setuid wrappers

The Sympa Community 2020-05-27 (Update)

Synopsis

A fix is available for a vulnerability discovered in Sympa web interface.

Systems Affected

• All versions of Sympa prior to 6.2.56

Problem Description

A vulnerability has been discovered in Sympa web interface by which attacker can execute arbitrary code with root privileges.

Sympa uses two sorts of setuid wrappers:

• FastCGI wrappers
• newaliases wrapper

The FastCGI wrappers (wwsympa-wrapper.fcgi and sympa_soap_server-wrapper.fcgi) were used to make the web interface running under privileges of a dedicated user.

The newaliases wrapper (sympa_newaliases-wrapper) allows Sympa to update the alias database with root privileges.

Since these setuid wrappers did not clear environment variables, if environment variables like PERL5LIB were injected, forged code might be loaded and executed under privileges of setuid-ed users.

For more details see References.

Impact

Attacker can execute arbitrary code with root privileges.

Workarounds

• Stop using FastCGI wrappers and remove them

  1. Modify configuration for HTTP server so that it will not use the wrapper. For detailed instructions see:

     • Configure HTTP server: Instruction by HTTP servers https://sympa-community.github.io/manual/install/configure-http-server.html#instruction-by-http-servers

  2. Remove executable files of FastCGI wrappers (replace $EXECCGIDIR below: See https://sympa-community.github.io/manual/layout.html):

     # cd $EXECCGIDIR
     # rm wwsympa-wrapper.fcgi
     # rm sympa_soap_server-wrapper.fcgi
     

  Note that newaliases wrapper may not be removed.

• No workaround has been known about some obsoleted systems requiring FastCGI wrapper, in particular Apache HTTP Server 2.2.x and earlier.

Solution

• Upgrade to version 6.2.56

  • Source distribution: sympa-6.2.56.tar.gz
  • Binary distributions: Check release information by distributors.

or, if you have installed Sympa using earlier version of source distribution,

• Apply a patch to the source, recompile wrappers and reinstall them:

  Patch for sympa-6.2 or later: sympa-6.2.54-sa-2020-002-r2.patch

  Patch for sympa-6.1.25: sympa-6.1.25-sa-2020-002-r2.patch

CVE Numbers

CVE-2020-10936

References

• Chatelain, Nicolas (2020). [CVE-2020-10936] SYMPA Privileges escalation to root.
• GitHub issue sympa-community/sympa#943: Security flaws in setuid wrappers
• Sympa 6.2.56 announce

Acknowledgements

The security flaw this advisory describes was reported by Nicolas Chatelain, Sysdream Labs.

Change log

• 2020-05-24

  Initial version published.

• 2020-05-27

  CVE Numbers: Confirmed that CVE-2020-10936 has been assigned.

  References: Adding report by Nicolas.

  Solution: Adding patch for Sympa 6.1.25