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CVE-2021-26081: REST API in Atlassian Jira Server and Jira Data Center before version 8.5.14, from version 8.6.0 before 8.1...

REST API in Atlassian Jira Server and Jira Data Center before version 8.5.14, from version 8.6.0 before 8.13.6, and from version 8.14.0 before 8.16.1 allows remote attackers to enumerate usernames via a Sensitive Data Exposure vulnerability in the `/rest/api/latest/user/avatar/temporary` endpoint.

MediumCVSS 5.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Some Jira Server and Jira Data Center versions exposed a REST endpoint that could let an unauthenticated remote attacker enumerate usernames. This is not system takeover, but username disclosure can support phishing, credential attacks, and reconnaissance against Jira-backed organizations.

Executive priority

Treat this as a moderate-priority hygiene and exposure-reduction item. It is unlikely to justify emergency response alone, but exposed Jira systems should be upgraded promptly because username disclosure can strengthen later credential and social-engineering attacks.

Technical view

CVE-2021-26081 is a sensitive data exposure issue in `/rest/api/latest/user/avatar/temporary` affecting Jira Server and Jira Data Center before 8.5.14, 8.6.0 before 8.13.6, and 8.14.0 before 8.16.1. CVSS 3.1 is 5.3: network, low complexity, no privileges, no user interaction, confidentiality impact only.

Likely exposure

Exposure is most relevant for internet-accessible or broadly reachable Jira Server/Data Center instances running the affected version ranges. Internal-only deployments still matter if untrusted users or compromised hosts can reach Jira.

Exploitation context

The source bundle does not indicate active exploitation, and KEV is false. The vulnerability is remotely reachable without authentication, but the documented impact is username enumeration rather than code execution, privilege escalation, or data modification.

Researcher notes

Evidence is limited to the CVE description and Atlassian issue reference in the bundle. The record names the vulnerable endpoint and version ranges, but does not provide CWE mapping, exploit telemetry, or detailed vendor mitigation text beyond fixed-version boundaries.

Mitigation direction

  • Upgrade affected Jira Server/Data Center instances to the applicable fixed version or later.
  • Prioritize internet-facing Jira instances and environments with weak account lockout controls.
  • If upgrade is delayed, check Atlassian guidance for supported compensating controls.
  • Reduce untrusted network access to Jira where business operations allow.

Validation and detection

  • Inventory Jira Server/Data Center instances and record exact versions.
  • Compare versions against the affected ranges listed in the CVE source bundle.
  • Confirm upgraded instances report 8.5.14, 8.13.6, 8.16.1, or later applicable fixed releases.
  • Review access logs for unusual unauthenticated requests to the named avatar endpoint.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-26081 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N3.91.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.3Medium
CVSS 3.1 vector shape for CVE-2021-26081Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
AtlassianJira Serverunspecified, 8.6.0, unspecified, 8.14.0, unspecifiedListed
AtlassianJira Data Centerunspecified, 8.6.0, unspecified, 8.14.0, unspecifiedListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.