CVE-2026-77255
HIGHDescription
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 to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 33% of all known CVEs.
References
Related Vulnerabilities
Other CWE-22 (Path Traversal) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2024-23897 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2023-32315 | High | 8.6 | 100% | KEV | Fix |
| CVE-2022-29464 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2021-26086 | Medium | 5.3 | 100% | KEV | Fix |
| CVE-2021-22005 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2020-5902 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2026-77255?
Upgrade mcp atlassian to 0.22.0 or later.
Is CVE-2026-77255 being actively exploited?
Not that we know of. CVE-2026-77255 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.41% is the estimated probability that it will be exploited in the next 30 days. That is higher than 33% of all scored CVEs.
How severe is CVE-2026-77255?
CVE-2026-77255 has a CVSS v3 base score of 8.6, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-77255 affect?
Published advisories record a fix for mcp atlassian (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2026-77255
Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-29.