CVE-2021-25641

CRITICAL

Apache Dubbo 2.5.0-2.6.8 & 2.7.0-2.7.7 Unauthenticated Deserialization via Serialization ID Tampering

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 2 public exploits for CVE-2021-25641. PoCs published by Dor-Tumarkin, l0n3rs.

AI-analyzed exploit summary This repository contains a functional exploit for CVE-2021-25641, a deserialization vulnerability in Apache Dubbo. The exploit leverages a FastJson gadget chain to achieve remote code execution (RCE) by sending a crafted payload over the Dubbo protocol.

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.

Exploits (2)

nomisec WORKING POC 53 stars
by Dor-Tumarkin · poc
https://github.com/Dor-Tumarkin/CVE-2021-25641-Proof-of-Concept

This repository contains a functional exploit for CVE-2021-25641, a deserialization vulnerability in Apache Dubbo. The exploit leverages a FastJson gadget chain to achieve remote code execution (RCE) by sending a crafted payload over the Dubbo protocol.

Classification
Working Poc 95%
Attack Type
Rce
Complexity
Moderate
Reliability
Reliable
Target: Apache Dubbo versions <= 2.7.3
No auth needed
Prerequisites: Network access to the target Dubbo service · Target must be running a vulnerable version of Apache Dubbo
devstral-2 · analyzed Feb 18, 2026 Full analysis →
nomisec SUSPICIOUS 4 stars
by l0n3rs · poc
https://github.com/l0n3rs/CVE-2021-25641

The repository claims to be an exploit for CVE-2021-25641 (Apache Dubbo deserialization vulnerability) but provides no actual exploit code, only a README with vague descriptions and a reference to an external JAR file. This is characteristic of a social engineering lure.

Classification
Suspicious 90%
Attack Type
Deserialization
Complexity
Theoretical
Reliability
Theoretical
Target: Apache Dubbo (versions 2.5.x, 2.6.0-2.6.9, 2.7.0-2.7.8)
No auth needed
Prerequisites: External JAR download
devstral-2 · analyzed Feb 18, 2026 Full analysis →

References (1)

Core 1

Scores

CVSS v3 9.8
EPSS 0.1767
EPSS Percentile 96.8%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Details

CWE
CWE-502
Status published
Products (3)
apache/dubbo 2.5.0 - 2.6.9
com.alibaba/dubbo 2.5.0 - 2.6.9Maven
org.apache.dubbo/dubbo 2.5.0 - 2.7.8Maven
Published Jun 01, 2021
Tracked Since Feb 18, 2026