A system hardening measure could be bypassed.

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Ubuntu Security Notice USN-4058-2
August 05, 2019

bash vulnerability
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 14.04 ESM
- Ubuntu 12.04 ESM

Summary:

A system hardening measure could be bypassed.

Software Description:
- bash: GNU Bourne Again SHell

Details:

USN-4058-1 fixed a vulnerability in bash. This update provides
the corresponding update for Ubuntu 12.04 ESM and Ubuntu 14.04 ESM.

Original advisory details:

 It was discovered that Bash incorrectly handled the restricted shell. An
 attacker could possibly use this issue to escape restrictions and execute
 any command.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 14.04 ESM:
  bash                            4.3-7ubuntu1.8+esm1

Ubuntu 12.04 ESM:
  bash                            4.2-2ubuntu2.8

In general, a standard system update will make all the necessary changes.

References:
  https://usn.ubuntu.com/4058-2
  https://usn.ubuntu.com/4058-1
  CVE-2019-9924