CVE-2021-34433Network attack vector

Server impersonation via omitted DTLS signature

Published Aug 20, 2021 · Updated Aug 4, 2024

Improper authentication in Eclipse Californium 2.0.0 through 2.6.4 and 3.0.0-M1 through 3.0.0-M3 allows remote attackers to impersonate DTLS servers. Client-side X.509 and RPK handshake processing treats an absent ServerKeyExchange signature as a reason to skip verification instead of rejecting the exchange. The attack requires an affected client to initiate a certificate-based DTLS connection to an attacker-controlled server, which is then accepted as authenticated.

CVSS severity7.5
High
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Eclipse Californium 2.0.0 through 2.6.4 and 3.0.0-M1 through 3.0.0-M3 allows remote attackers to impersonate DTLS servers. Client-side X.509 and RPK handshake processing treats an absent ServerKeyExchange signature as a reason to skip verification instead of rejecting the exchange. The attack requires an affected client to initiate a certificate-based DTLS connection to an attacker-controlled server, which is then accepted as authenticated.

The record

CVE
CVE-2021-34433
Published
Aug 20, 2021
Updated
Aug 4, 2024
Vendor
The Eclipse Foundation
Product
Eclipse Californium
Classifications
CWE-322, CWE-347, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.0.0 <unspecified
  2. Affected versionversion=3.0.0-M1 <unspecified
  3. Affected versionversion=unspecified <=2.6.4
  4. Affected versionversion=unspecified <=3.0.0-M3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Eclipse Foundation · Eclipse Californiumversion=2.0.0 <unspecified; version=3.0.0-M1 <unspecified; version=unspecified <=2.6.4; version=unspecified <=3.0.0-M3

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-322Key Exchange without Entity Authentication
CWE-347Improper Verification of Cryptographic Signature
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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