How severe is CVE-2026-77255?

CVE-2026-77255 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-77255 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-77255?

CVE-2026-77255 affects Mcp-atlassian Mcp Atlassian. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-77255?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-77255 published?

CVE-2026-77255 was published on 2026-09-22 and last updated on 2026-09-29.

CVE-2026-77255

CVE-2026-77255 is a high-severity vulnerability in Mcp-atlassian Mcp Atlassian with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-22.

Key facts

Severity: High (CVSS 3.x base score 8.6)
EPSS exploit prediction: 0% (34th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-22
Affected product: Mcp-atlassian Mcp Atlassian
Published: 2026-09-22
Last modified: 2026-09-29

Description

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the Jira update_issue attachments argument is converted into local paths and routed to the attachment upload implementation without workspace validation. A caller can make the MCP server read arbitrary local files and attach them to a Jira issue, using the server as a confused deputy to exfiltrate the contents. The advisory traces the vulnerable input and processing flow through jira update_issue, attachments, upload_attachment, and file_path, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

Frequently asked questions

What is CVE-2026-77255?: MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the Jira update_issue attachments argument is converted into local paths and routed to the attachment upload implementation without workspace validation. A caller can make the MCP server read arbitrary local files and attach them to a Jira issue, using the server as a confused deputy to exfiltrate the contents. The advisory traces the vulnerable input and processing flow through jira update_issue, attachments, upload_attachment, and file_path, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
How severe is CVE-2026-77255?: CVE-2026-77255 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-77255 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-77255?: CVE-2026-77255 affects Mcp-atlassian Mcp Atlassian. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-77255?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-77255 published?: CVE-2026-77255 was published on 2026-09-22 and last updated on 2026-09-29.

References

Affected products (1)

cpe:2.3:a:mcp-atlassian:mcp_atlassian:*:*:*:*:*:*:*:*

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