CVE-2021-26081Network attack vector

Unauthenticated username enumeration via temporary-avatar endpoint

Published Jul 20, 2021 · Updated Oct 11, 2024

Username enumeration in affected Atlassian Jira Server and Jira Data Center releases allows remote attackers to discover account names. The /rest/api/latest/user/avatar/temporary endpoint reveals whether a supplied username belongs to an existing account, but Atlassian has not published the responsible implementation error. No authentication or user interaction is required; affected versions are before 8.5.14, 8.6.0 through 8.13.5, and 8.14.0 through 8.16.0, and disclosure is limited to Jira usernames.

CVSS severity5.3
Medium
EPSS probability1.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Username enumeration in affected Atlassian Jira Server and Jira Data Center releases allows remote attackers to discover account names. The /rest/api/latest/user/avatar/temporary endpoint reveals whether a supplied username belongs to an existing account, but Atlassian has not published the responsible implementation error. No authentication or user interaction is required; affected versions are before 8.5.14, 8.6.0 through 8.13.5, and 8.14.0 through 8.16.0, and disclosure is limited to Jira usernames.

The record

CVE
CVE-2021-26081
Published
Jul 20, 2021
Updated
Oct 11, 2024
Vendor
Atlassian
Product
Jira Server
Classifications
T1589
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 11, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=0 <8.5.14
  2. Affected versionversion=8.14.0 <8.16.1
  3. Affected versionversion=8.14.0 <unspecified
  4. Affected versionversion=8.6.0 <8.13.6
  5. Affected versionversion=8.6.0 <unspecified
  6. Affected versionversion=unspecified <8.13.6
  7. Affected versionversion=unspecified <8.16.1
  8. Affected versionversion=unspecified <8.5.14

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Atlassian · Jira Serverversion=0 <8.5.14; version=8.14.0 <8.16.1; version=8.14.0 <unspecified; version=8.6.0 <8.13.6; version=8.6.0 <unspecified; version=unspecified <8.13.6; version=unspecified <8.16.1; version=unspecified <8.5.14
Atlassian · Jira Data Centerversion=0 <8.5.14; version=8.14.0 <8.16.1; version=8.14.0 <unspecified; version=8.6.0 <8.13.6; version=8.6.0 <unspecified; version=unspecified <8.13.6; version=unspecified <8.16.1; version=unspecified <8.5.14

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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

T1589Gather Victim Identity Information

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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