CVE-2021-34580Network attack vector

Backend user enumeration via login response discrepancy

Published Oct 27, 2021 · Updated Sep 17, 2024

Response discrepancy in MB connect line mbCONNECT24 and mymbCONNECT24 2.9.0 and earlier allows remote attackers to enumerate backend users. The login workflow returns distinguishable server responses when crafted invalid attempts name valid rather than nonexistent backend accounts. No authentication or user interaction is required, and the reported consequence is limited to discovering valid backend usernames.

CVSS severity7.5
High
EPSS probability1.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Response discrepancy in MB connect line mbCONNECT24 and mymbCONNECT24 2.9.0 and earlier allows remote attackers to enumerate backend users. The login workflow returns distinguishable server responses when crafted invalid attempts name valid rather than nonexistent backend accounts. No authentication or user interaction is required, and the reported consequence is limited to discovering valid backend usernames.

The record

CVE
CVE-2021-34580
Published
Oct 27, 2021
Updated
Sep 17, 2024
Vendor
MB connect line
Product
mbCONNECT24
Classifications
CWE-203, CWE-204, T1087
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=2.9.0 <=2.9.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

MB connect line · mbCONNECT24version=2.9.0 <=2.9.0
MB connect line · mymbCONNECT24version=2.9.0 <=2.9.0

Published CVSS scores

7.5CERT@VDECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/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-203Observable Discrepancy
CWE-204Observable Response Discrepancy
T1087Account Discovery

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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