Medium [CVE-2020-12265 +1] path traversal via indexOf containment bypass allows arbitrary file write (bypass of CVE-2020-12265 fix)

decompress before 4.2.2 contains an improper path containment check that enables directory traversal and arbitrary file write. The safeMakeDir function (index.js line 29) and the extraction path validation (index.js line 106) use String.indexOf() to verify the resolved path is within the output directory: realDestinationDir.indexOf(realOutputPath)!== 0.

This check is flawed because it does not enforce a path separator boundary. For example, "/tmp/app_config".indexOf("/tmp/app") returns 0, incorrectly passing the check even though /tmp/app_config is outside /tmp/app.

Combined with the unvalidated symlink creation in the same package, an attacker can write arbitrary files to directories adjacent to the extraction target. This is a bypass of the fix for CVE-2020-12265.

The correct check requires appending a path separator: realParentPath.indexOf(realOutputPath + path.sep)!== 0. A flaw was found in the `decompress` component.

Red Hat's assessment aligns with the CVSSv3.1 base score of 6.2 (Moderate) published by CVE.org/CISA for this issue. The vulnerable safeMakeDir/indexOf path-containment check described in this CVE exists only in decompress 4.2.1, the final release that addressed the earlier CVE-2020-12265 path traversal issue.

Affected products named by the advisory: Red Hat Hardened Images; Red Hat Build of Keycloak.