CVE-2021-25641 — dubbo
CRITICALCVE-2021-25641 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in org.apache.dubbo:dubbo. 4 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for org.apache.dubbo:dubbo — see the affected versions and patch details below.
Deserializer tampering in Apache Dubbo
EPSS Exploitation Probability
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
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 | 2.7.8org.apache.dubbo:dubbo:2.7.8 |
| ☕Maven | com.alibaba:dubbo | ≥ 2.5.0&&< 2.6.9 | 2.6.9com.alibaba:dubbo:2.6.9 |
Affected Products
dubboapacheResearch 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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.
Frequently Asked Questions
Is CVE-2021-25641 in your dependencies?
Find it across Maven, including transitive dependencies.