CVE-2021-20556Network attack vector

Username enumeration via differentiated authentication errors

Published May 3, 2024 · Updated Aug 3, 2024

Information disclosure in IBM Cognos Controller 10.4.1, 10.4.2, and 11.0.0 allows remote attackers to enumerate usernames. The authentication interface returns different error messages depending on whether a submitted username exists, creating a response oracle for account discovery. Network access without authentication or user interaction is sufficient; the reported consequence is limited to disclosure of valid usernames.

CVSS severity5.3
Medium
EPSS probability0.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in IBM Cognos Controller 10.4.1, 10.4.2, and 11.0.0 allows remote attackers to enumerate usernames. The authentication interface returns different error messages depending on whether a submitted username exists, creating a response oracle for account discovery. Network access without authentication or user interaction is sufficient; the reported consequence is limited to disclosure of valid usernames.

The record

CVE
CVE-2021-20556
Published
May 3, 2024
Updated
Aug 3, 2024
Vendor
IBM
Product
IBM Cognos Controller
Classifications
CWE-204, CWE-203, T1087
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 3, 2024CVE publishedPublication date reported by the CVE source.
  2. 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?

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

  1. Affected versionversion=10.4.1
  2. Affected versionversion=10.4.1, 10.4.2, 11.0.0
  3. Affected versionversion=10.4.2
  4. Affected versionversion=11.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

IBM · IBM Cognos Controllerversion=10.4.1; version=10.4.1, 10.4.2, 11.0.0; version=10.4.2; version=11.0.0

Published CVSS scores

5.3IBM CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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-204Observable Response Discrepancy
CWE-203Observable 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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