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DubboApplication · Apache

CVE-2021-25641

CRITICAL · 9.8 CVSS v3.1 Published 2021-06-01
Fix available
A fix is available. Upgrade to 2.6.9 / 2.7.8 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In Apache Dubbo servers before 2.7.8 or 2.6.9, an attacker can tamper with serialization byte preamble flags to force the provider to use a weak deserializer (Kryo or FST) instead of the server-specified protocol. This allows unauthenticated remote attackers to exploit known deserialization vulnerabilities in these weak serializers for RCE.

MitigationUpgrade Apache Dubbo to version 2.7.8 or 2.6.9 or later. If upgrading is not immediately possible, ensure Kryo, FST, and other weak deserializers are not in the application classpath.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
DubboApplication
Affected:>= 2.5.0, < 2.6.9>= 2.7.0, < 2.7.8

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Apache Dubbo version
    Examine the dubbo JAR files in your application deployment or check the version in your dependency management file (pom.xml, build.gradle, or the MANIFEST.MF inside dubbo JARs)
    Affected if Version is 2.5.0 through 2.6.8, or 2.7.0 through 2.7.7
  2. Detect Kryo deserializer presence
    Search application classpath for kryo JAR (typically kryo-*.jar) or examine build dependencies for com.esotericsoftware:kryo
    Affected if Kryo library is present in the runtime classpath
  3. Detect FST deserializer presence
    Search application classpath for fst JAR (typically fst-*.jar) or examine build dependencies for org.nustaq:fst
    Affected if FST library is present in the runtime classpath
  4. Check serialization configuration
    Review Dubbo protocol and serialization configuration files or code for any explicit use of serialization filters, Hessian, or Kryo/FST settings
    Affected if Serialization is configured to allow flexible serializer selection or explicitly uses Kryo/FST

Affected if running Dubbo version 2.5.0-2.6.8 or 2.7.0-2.7.7 AND having either Kryo or FST in the application classpath with configurable serialization.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.6.9 / 2.7.8 or later
Fixed in 2.6.92.7.8
Interim mitigation

Upgrade Apache Dubbo to version 2.7.8 or 2.6.9 or later. If upgrading is not immediately possible, ensure Kryo, FST, and other weak deserializers are not in the application classpath.

Recommended fix High confidence

Upgrade to Dubbo 2.7.8+ (if using 2.7.x) or 2.6.9+ (if using 2.6.x); recommend latest stable in respective branch for additional security fixes

  1. Identify the current Dubbo version in your project by checking pom.xml or build.gradle for the dubbo dependency version
  2. For Dubbo 2.7.x users: Upgrade to version 2.7.8 or later (recommended: latest 2.7.x stable release)
  3. For Dubbo 2.6.x users: Upgrade to version 2.6.9 or later (recommended: latest 2.6.x stable release)
  4. Update the version in your dependency management file (pom.xml: <dubbo.version>...</dubbo.version> or build.gradle: implementation 'org.apache.dubbo:dubbo:x.x.x')
  5. Run mvn clean install or gradle build to verify the upgrade does not break compilation
  6. Test the application thoroughly, specifically RPC communication between Dubbo clients and providers
  7. Alternatively, if upgrading is not immediately possible, ensure only strong serialization methods (like Hessian) are enabled and weak serializers (Kryo, FST) are excluded from the classpath by reviewing dependencies
Caveat Review Dubbo migration guides when crossing major version boundaries; minor version upgrades within 2.6.x or 2.7.x typically have minimal breaking changes but test thoroughly

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Dubbo Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA3.0 h
18.0 hours of engineering $3,060
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-25641 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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