Insecure temporary file in Netflix OSS Hollow

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.4 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2021-28099: 0.25% estimated exploitation activity in the next 30 days; percentile 16.60 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

ID: NFLX-2021-001 Title: Local information disclosure in Hollow Release Date: 2021-03-23 Credit: Security Researcher @JLLeitschuh Overview Security researcher @JLLeitschuh reported that Netflix Hollow (a Netflix OSS project available here: https://github.com/Netflix/hollow) writes to a local temporary directory before validating the permissions on it. Impact An attacker with the ability to create directories and set permissions on the local filesystem could pre-create this directory and read or modify anything written there by the Hollow process. Description Since the Files.exists(parent) is run before creating the directories, an attacker can pre-create these directories with wide permissions. Additionally, since an insecure source of randomness is used, the file names to be created can be deterministically calculated. Workarounds and Fixes Avoid running Hollow in configurations that share a filesystem with less-trusted processes. May be fixed in a future release.

Published by the source

29 Mar 2021, 18:25 UTC

Last modified by the source

8 Aug 2023, 19:54 UTC

Source last checked

26 Oct 2026, 16:11 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9295-mhf3-v33m

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# Patch Next advisory brief: CVE-2021-28099

Advisory: Insecure temporary file in Netflix OSS Hollow
IDs: CVE-2021-28099, GHSA-9295-mhf3-v33m
Record: https://patchnext.com/advisories/cve-2021-28099 (revision 1, source checked 26 Oct 2026, 16:11 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.netflix.hollow:hollow: affected <= 6.1.0

## Suggested inspection (read-only)
- Maven com.netflix.hollow:hollow: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on com.netflix.hollow:hollow.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9295-mhf3-v33m (GitHub-reviewed advisory GHSA-9295-mhf3-v33m lists affected ranges: Maven com.netflix.hollow:hollow >=0 <=6.1.0)

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