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posted by n1 on Thursday September 25 2014, @01:59AM   Printer-friendly
from the well,-that's-not-ideal dept.

Ars reports that a new bug has been found in GNU Bash allows remote attackers to execute arbitrary code by setting the process trailing strings after function definitions in the values of environment variables.

This bug is reported to be present in RHEL (ver 4 through 7), Fedora, CentOS (ver 5 through 7), Ubuntu (ver 10.04 LTS, 12.04 LTS, and 14.04 LTS), Debian, and even OS X Mavericks.

This bug is exploitable through Apache servers with mod_cgi and mod_cgid loaded, OpenSSH, malicious DHCP servers in a compromised wireless access point through dhclient, as well as the CUPS printing system.

The Ars also includes a simple single liner that will test your setup for the newly found discovery:

env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

A vulnerable system will output the following:

vulnerable
 this is a test

While a patched or unaffected system outputs:

bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'
this is a test

A patch is already out, so administrators are advised to update Bash.

Editor's Update: Security Engineer Tavis Ormandy has said "The bash patch seems incomplete to me, function parsing is still brittle".

$ env X='() { (a)=>\' sh -c "echo date"; cat echo

 
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  • (Score: 0) by Anonymous Coward on Thursday September 25 2014, @01:58PM

    by Anonymous Coward on Thursday September 25 2014, @01:58PM (#98221)

    On the other hand, for scripts you would use /bin/sh which at least on Debian systems is not bash. Also system() uses /bin/sh. So any Debian system using properly written scripts should be fine (unless dash is also vulnerable).

  • (Score: 2) by choose another one on Thursday September 25 2014, @03:14PM

    by choose another one (515) Subscriber Badge on Thursday September 25 2014, @03:14PM (#98269)

    Yep, /bin/sh != bash would be a start.

    Not sure how much that will break on other systems. Might be better to ban bash from non-interactive use, or get rid of it entirely, the whole idea of parsing environment variables as code is an exploit waiting to happen - putting band-aids on the parser will be a temporary and fragile fix (as already shown).