CVE-2012-0955: 
Linux Debian vulnerability analysis and mitigation

CVE-2012-0955 affects software-properties, specifically related to incorrect TLS certificate validation in softwareproperties/ppa.py. The vulnerability was discovered in versions before 0.92, where the software didn't properly check TLS certificates under Python2 and only checked certificates under Python3 if a valid certificate bundle was provided (NVD, Launchpad Bug).

The vulnerability stems from improper certificate validation implementation during the Python3 migration of software-properties. Under Python2, urllib2 did not perform SSL certificate checking, and under Python3, urllib.request only performed certificate checking if the cafile pointed to a valid certificate bundle. The CVSS v3.1 base score is 7.4 (HIGH) with vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N, indicating potential for high impact on confidentiality and integrity (NVD).

The vulnerability could allow a person-in-the-middle attacker to compromise a remote system by exploiting the incorrect SSL certificate validation. This essentially reverted a previous security fix (CVE-2011-4407) and left systems vulnerable to MITM attacks (Launchpad Bug).

The vulnerability is exploitable through a man-in-the-middle attack scenario, taking advantage of the improper certificate validation in the software. The attack vector is network-based, requiring no privileges or user interaction, though with high attack complexity (NVD).

The vulnerability was fixed in software-properties version 0.92. The fix involved reinstating pycurl for getting PPA information from Launchpad, as it could properly verify SSL certificates with Python2. Additionally, LAUNCHPAD_PPA_CERT was set to a valid path to the system CA certificates bundle for use with urllib and pycurl (Launchpad Merge).