CVE-2021-33831Known exploitationPublic exploitNetwork attack vector

Contact-tracing disruption via unlimited guest registration

Published Sep 7, 2021 · Updated Aug 3, 2024

Resource exhaustion in TH Wildau COVID-19 Contact Tracing through 2021-09-01 allows remote attackers to disrupt infection tracing. The /api/account/register endpoint accepts unlimited automated guest registrations without CAPTCHA, throttling, or email and phone verification. An attacker can obtain the required CSRF cookie and guest session through public endpoints, then create 500 fake users and room check-ins within 2,500 seconds, making legitimate contact chains impractical to trace.

CVSS severity6.5
Medium
EPSS probability2.02%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in TH Wildau COVID-19 Contact Tracing through 2021-09-01 allows remote attackers to disrupt infection tracing. The /api/account/register endpoint accepts unlimited automated guest registrations without CAPTCHA, throttling, or email and phone verification. An attacker can obtain the required CSRF cookie and guest session through public endpoints, then create 500 fake users and room check-ins within 2,500 seconds, making legitimate contact chains impractical to trace.

The record

CVE
CVE-2021-33831
Published
Sep 7, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-770, T1499.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 31, 2021Exploitation reportedSuccessful deployment exploit demonstration
  2. Sep 7, 2021CVE publishedPublication date reported by the CVE source.
  3. Aug 3, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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
Privilegesauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Application Exhaustion Flood

Public exploit references

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

Reported exploitation

Technologies

Your stack

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Your stack

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