CVE-2026-39245

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

CVE-2026-39245Source published Jul 9, 2026Source updated Jul 9, 2026

This bulletin covers 2 CVEs. The products, versions, score and guidance below describe the bulletin; check its source for applicability to this specific CVE.

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…

Affected products in this advisory

• Red Hat Hardened Images
• Red Hat Build of Keycloak

Source-reported affected versions

• < 4.2.2

Source-reported fixed versions

• dotnet8-0-main-8.0.128-1.1.hum1
• RHSA-2026:37577

Mitigation guidance

• No upstream fix is available. The decompress package is unmaintained and no 4.2.2 release was ever published. Applications should avoid extracting untrusted archives with decompress 4.2.1, or migrate to a maintained fork such as @xhmikosr/decompress.