CVE-2021-25641
CRITICALDeserializer tampering in Apache Dubbo
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
org.apache.dubbo:dubbo☕com.alibaba:dubboReal-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
Each Apache Dubbo server will set a serialization id to tell the clients which serialization protocol it is working on. But for Dubbo versions before 2.7.8 or 2.6.9, an attacker can choose which serialization id the Provider will use by tampering with the byte preamble flags, aka, not following the server's instruction. This means that if a weak deserializer such as the Kryo and FST are somehow in code scope (e.g. if Kryo is somehow a part of a dependency), a remote unauthenticated attacker can tell the Provider to use the weak deserializer, and then proceed to exploit it.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.dubbo:dubbo | ≥ 2.5.0&&< 2.7.8 | 2.7.8 |
| ☕Maven | com.alibaba:dubbo | ≥ 2.5.0&&< 2.6.9 | 2.6.9 |
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.apache.dubbo:dubbo. 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.apache.dubbo:dubbo to 2.7.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-25641 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 CVE-2021-25641 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 CVE-2021-25641. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-25641 in your dependencies?
O3 detects CVE-2021-25641 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.