snap-confine in snapd before 2.38 incorrectly set the ownership of a snap application to the uid and gid of the first calling user. Consequently, that user had unintended access to a private /tmp directory.
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 | * | 2.38 (excluding) |
| Snapd | Ubuntu | bionic | * |
| Snapd | Ubuntu | cosmic | * |
| Snapd | Ubuntu | disco | * |
| Snapd | Ubuntu | esm-infra/bionic | * |
| Snapd | Ubuntu | esm-infra/xenial | * |
| Snapd | Ubuntu | trusty | * |
| 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.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/132.html
- https://cwe.mitre.org/data/definitions/17.html
- https://cwe.mitre.org/data/definitions/35.html
- https://cwe.mitre.org/data/definitions/76.html
References
- http://www.openwall.com/lists/oss-security/2019/04/25/7
- https://github.com/snapcore/snapd/commit/bdbfeebef03245176ae0dc323392bb0522a339b1
- https://www.openwall.com/lists/oss-security/2019/04/18/4
- http://www.openwall.com/lists/oss-security/2019/04/25/7
- https://github.com/snapcore/snapd/commit/bdbfeebef03245176ae0dc323392bb0522a339b1
- https://www.openwall.com/lists/oss-security/2019/04/18/4