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NVD / CVE Program· CNA apache

CVE-2021-25641: Dubbo Zookeeper does not check serialization id

Noroxi assessment

Priority: Plan (action score 45/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 21.2% (FIRST EPSS); higher than 97.5% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: com.alibaba:dubbo (Maven) 2.6.9; org.apache.dubbo:dubbo (Maven) 2.7.8.

Add it to your regular patch cycle. Upgrade to com.alibaba:dubbo (Maven) 2.6.9; org.apache.dubbo:dubbo (Maven) 2.7.8 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

CriticalCVSS 9.8 · v3.1—Proof of concept Fix available
Published
Jun 1, 2021
Updated
Jun 16, 2026
EPSS
21.2% · 97th percentile

Report tools

JSON

Action score

45

Plan

Add it to your regular patch cycle.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
6 / 30 · 21.2%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
apachedubbo

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • apache dubbo2.5.0 and later · before 2.6.9
  • apache dubbo2.7.0 and later · before 2.7.8

Versions reported by the vendor

Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.

  • Apache Software Foundation Apache Dubbo

    • Apache Dubbo 2.7.x and later · before 2.7.8affected
    • Apache Dubbo 2.6.x and later · before 2.6.9affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Mavencom.alibaba:dubbofrom 2.5.0 · before 2.6.92.6.9
Mavenorg.apache.dubbo:dubbofrom 2.5.0 · before 2.7.82.7.8

Same product

apache: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-30181Apache Dubbo RCE on customers via Script route poisoning (Nashorn script injection)
    57Plan
  • CVE-2021-30180Apache Dubbo RCE on customers via Condition route poisoning (Unsafe YAML unmarshaling)
    57Plan
  • CVE-2019-17564Unsafe deserialization occurs within a Dubbo application which has HTTP remoting enabled.
    50Plan

Published before and after this one in the same product

  • ← EarlierCVE-2020-11995Jan 11, 2021 · Apache Dubbo default deserialization protocol Hessian2 cause CRE
    41Plan
  • ← EarlierCVE-2021-25640Jun 1, 2021 · Open Redirect or SSRF vulnerability usage of parseURL
    25Monitor
  • Later →CVE-2021-30179Jun 1, 2021 · Apache Dubbo Pre-auth RCE via Java deserialization in the Generic filter
    40Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Maven:com.alibaba:dubbo2.6.9Package registry (OSV)
Maven:org.apache.dubbo:dubbo2.7.8Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×2

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:532021-06-06
Proof-of-concept repository on GitHubstars:42022-11-10

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+5 d
  3. TodayOct 29, 2026+1977 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-502 · Deserialization of Untrusted Data

CVSS vector

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

nvd-primary

Root cause

Data received over the network is deserialized into the language’s native object format without verifying its source. Code paths inside the object can be triggered during deserialization.

The bug in code

The whole CWE-502 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

python
payload = sock.recv(65536)job = pickle.loads(payload)

Fixed

python
payload = sock.recv(65536)if not hmac.compare_digest(sign(payload), header_sig):    raise PermissionError("invalid signature")job = JobSchema.validate(json.loads(payload))

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records