GHSA-5662-cv6m-63wh melange's world-writable permissions expose SBOM files to potential image tampering

• Go chainguard.dev/melange: >= 0.23.0, < 0.29.5 → fixed in 0.29.5

It was discovered that the SBOM files generated by melange in apks had file system permissions mode 666: ``` $ apkrane ls https://packages.wolfi.dev/os/x86_64/APKINDEX.tar.gz -P hello-wolfi --full --latest | xargs wget -q -O - | tar tzv 2>/dev/null var/lib/db/sbom drwxr-xr-x root/root 0 2025-06-23 14:17 var/lib/db/sbom -rw-rw-rw- root/root 3383 2025-06-23 14:17 var/lib/db/sbom/hello-wolfi-2.12.2-r1.spdx.json ``` This issue was introduced in commit 1b272db ("Persist workspace filesystem throughout package builds (#1836)") (v0.23.0). Impact This potentially allows an unprivileged user to tamper with apk SBOMs on a running image, potentially confusing security scanners. An attacker could also perform a DoS under special circumstances. Patches This issue was addressed in melange in e29494b ("fix: tighten up permissions for written SBOM files and signature tarballs (#2086)") (v0.29.5). Acknowledgements Thanks to Cody Harris H2O.ai and Markus Boehme for independently reporting this issue.