CVE-2019-11503

snap-confine as included in snapd before 2.39 did not guard against symlink races when performing the chdir() to the current working directory of the calling user, aka a cwd restore permission bypass.

Weakness

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Affected Software

Name	Vendor	Start Version	End Version
Snapd	Canonical	*	2.39 (excluding)
Snapd	Ubuntu	bionic	*
Snapd	Ubuntu	cosmic	*
Snapd	Ubuntu	disco	*
Snapd	Ubuntu	eoan	*
Snapd	Ubuntu	esm-infra/bionic	*
Snapd	Ubuntu	esm-infra/xenial	*
Snapd	Ubuntu	trusty	*
Snapd	Ubuntu	trusty/esm	*
Snapd	Ubuntu	upstream	*
Snapd	Ubuntu	xenial	*

Potential Mitigations

Follow the principle of least privilege when assigning access rights to entities in a software system.
Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

NVD	https://nvd.nist.gov/vuln/detail/CVE-2019-11503
CWE	https://cwe.mitre.org/data/definitions/59.html

Improper Link Resolution Before File Access ('Link Following')

Weakness

Affected Software

Potential Mitigations

References

CVE-2019-11503

Improper Link Resolution Before File Access ('Link Following')

Weakness

Affected Software

Potential Mitigations

Related Attack Patterns

References