melange allows users to build apk packages using declarative pipelines. Starting in version 0.23.0 and prior to version 0.29.5, SBOM files generated by melange in apks had file system permissions mode 666. 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. Version 0.29.5 fixes the issue.

Affected: Go: chainguard.dev/melange

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](https://github.com/chainguard-dev/melange/releases/tag/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](https://github.com/chainguard-dev/melange/releases/tag/v0.29.5)).

## Acknowledgements

Thanks to Cody Harris [H2O.ai](https://h2o.ai/) and Markus Boehme for independently reporting this issue.

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