Billion laughs attack (XML bomb)

Exploitation

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

CVSS

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

EPSS

• CVE-2021-32623: 1.25% estimated exploitation activity in the next 30 days; percentile 69.51 (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.

Impact Opencast is vulnerable to the Billion laughs attack which allows an attacker to easily execute a (seemingly permanent) denial of service attack, essentially taking down Opencast using a single HTTP request. Consider an XML file (createMediaPackage.xml) like this: Throwing this at Opencast will cause Opencast to parse the XML and expand the Lorem Ipsum about 100 000 times, instantly consuming a huge amount of memory: Additional notes: - You can likely use other endpoints accepting XML (this was just the first one I tried) and depending on how much memory you want to consume, you might want to enlarge the lorem ipsum text. - Opencast's XML parser does limit the expansion to 100 000 times, already limiting the attack. Nevertheless, this can already harm the system. - To exploit this, users need to have ingest privileges, limiting the group of potential attackers Patches The problem has been fixed in Opencast 9.6. Older versions of Opencast are not patched sue to the extent of…

Published by the source

17 Jun 2021, 20:11 UTC

Last modified by the source

1 Feb 2023, 05:05 UTC

Source last checked

26 Oct 2026, 16:06 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9gwx-9cwp-5c2m

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# Patch Next advisory brief: CVE-2021-32623

Advisory: Billion laughs attack (XML bomb)
IDs: CVE-2021-32623, GHSA-9gwx-9cwp-5c2m
Record: https://patchnext.com/advisories/cve-2021-32623 (revision 1, source checked 26 Oct 2026, 16:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.opencastproject:opencast-kernel 9.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.opencastproject:opencast-kernel: affected < 9.6; fixed in 9.6

## Suggested inspection (read-only)
- Maven org.opencastproject:opencast-kernel: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.opencastproject:opencast-kernel.
- 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-9gwx-9cwp-5c2m (GitHub-reviewed advisory GHSA-9gwx-9cwp-5c2m lists affected ranges: Maven org.opencastproject:opencast-kernel >=0 <9.6)

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