CVE-2019-3902

A flaw was found in Mercurial before 4.9. It was possible to use symlinks and subrepositories to defeat Mercurials path-checking logic and write files outside a repository.

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

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

• https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3902
• https://lists.debian.org/debian-lts-announce/2019/04/msg00024.html
• https://lists.debian.org/debian-lts-announce/2020/07/msg00032.html
• https://usn.ubuntu.com/4086-1/
• https://www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.9_.282019-02-01.29