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

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.

Published: 2021-06-01 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-25641 is rated High Risk (77.7/100): CVSS Critical severity, with high exploitation likelihood (EPSS 74.62%, 99th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +3.95% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-25641

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-11-21 70.67% 74.62% +3.95%
2 2025-11-18 74.62% 70.67% -3.95%
3 2025-11-11 — 74.62% —

Full EPSS history (25 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-25641

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-25641

GitHub Security Advisory for CVE-2021-25641

GHSA-v2rg-8cwr-75g8 · Severity: critical · Ecosystem: maven — Deserializer tampering in Apache Dubbo

Affected software / configurations for CVE-2021-25641

Vendor Product Version Raw CPE
apache dubbo >= 2.5.0, < 2.6.9 cpe:2.3:a:apache:dubbo:*:*:*:*:*:*:*:*
apache dubbo >= 2.7.0, < 2.7.8 cpe:2.3:a:apache:dubbo:*:*:*:*:*:*:*:*

References for CVE-2021-25641

cvelogic Threat Intelligence