Pierluigi Paganini May 09, 2019

Since December 2015, Alpine Linux Docker images have been shipped with hardcoded credentials, a NULL password for the root user. 

Security researchers from Cisco revealed that Alpine Linux Docker images distributed via the official Docker Hub portal since December 2015 have been using a NULL password for the root account,

The NULL password for the root account was included in the Official Alpine Linux Docker images since v3.3. The bug received a CVSS score of 9.8, it affects Alpine Docker versions 3.3 to 3.9, including Alpine Docker Edge. 

“Versions of the Official Alpine Linux Docker images (since v3.3) contain a NULL password for the root user. This vulnerability appears to be the result of a regression introduced in December 2015.” reads the blog post published by Talos group. “Due to the nature of this issue, systems deployed using affected versions of the Alpine Linux container that utilize Linux PAM, or some other mechanism that uses the system shadow file as an authentication database, may accept a NULL password for the root user.”

The issue was first reported in August 2015 and patched in November, evidently, it was re-introduced in December 2015.

The NULL passoword is present in the /etc/shadow file of the affected builds of the Alpine Docker Image.

“In builds of the Alpine Docker Image (>=3.3) the /etc/shadow file contains a blank field in place of the encrypted password (sp_pwdp in the context of the spwd struct returned by getspent.” continues Talos.

$ for i in seq 1 9; do echo -n "date - Alpine Docker 3.$i - "; docker run -it alpine:3.$i head -n 1 /etc/shadow ; done"

Talos reported the flaw to Alpine Linux in February, experts explained that

Anyway, the good news is that the root account should be explicitly disabled in Docker images that are based on the vulnerable versions. 

“The likelihood of exploitation of this vulnerability is environment-dependent, as successful exploitation requires that an exposed service or application utilise Linux PAM, or some other mechanism which uses the system shadow file as an authentication database,” Talos concludes.

Pierluigi Paganini

(SecurityAffairs – hardcoded credentials, Alpine Linux Docker)

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