CVE-2026-77256

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit probability: 0.3% (25th percentile of EPSS-scored CVEs). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this weekElevated
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 6.5Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other local users can read the backup and retain Atlassian access through the refresh token. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens_to_file, refresh_token, access_token, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
45
EG Risk 45/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation40% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
25th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

September 22, 2026

Last Modified

September 28, 2026

Advisory Details (4)

Auto-updated Sep 22, 2026
🔬 Proof of concept available. Patch available. Sources: github_pr, github_commit, github_release, github.
github_release Patch Available

v0.22.0

Patch available: sooperset/mcp-atlassian v0.22.0

https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
github_commit Patch Available

commit b041733473f9 (sooperset/mcp-atlassian)

Patch available: sooperset/mcp-atlassian v0.22.0 (contains commit b041733473f9)

https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
github_pr Patch Available

Security hardening across attachment, transport, SSRF, authorization, filter, and OAuth layers

Patch available: sooperset/mcp-atlassian v0.22.0 (PR #1448 merged 2026-07-10)

https://github.com/sooperset/mcp-atlassian/pull/1448
github Patch Available🟡 PoC Available

OAuth refresh-token backup file is world-readable under default Unix umask · Advisory · sooperset/mcp-atlassian · GitHub

https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-76pr-5669-3xf5

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 14× in last 7d / 26× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-10-04 13:07 UTCEG score recompute
  2. 2026-10-03 14:26 UTCEPSS rescore
  3. 2026-10-03 13:09 UTCEG score recompute
  4. 2026-10-02 13:15 UTCEG score recompute
  5. 2026-10-01 19:50 UTCEPSS rescore
  6. 2026-10-01 13:18 UTCEG score recompute
  7. 2026-09-30 13:25 UTCEG score recompute
  8. 2026-09-29 15:24 UTCEPSS rescore
  9. 2026-09-29 13:25 UTCEG score recompute
  10. 2026-09-28 13:52 UTCEPSS rescore
  11. 2026-09-28 13:29 UTCEG score recompute▼ 1.80
  12. 2026-09-28 13:29 UTCNVD updateCVSS v3 → 6.5 · severity → MEDIUM
  13. 2026-09-27 22:26 UTCEG score recompute
  14. 2026-09-27 13:48 UTCEPSS rescore
  15. 2026-09-27 00:14 UTCEG score recompute
  16. 2026-09-26 15:59 UTCEPSS rescore
  17. 2026-09-26 01:58 UTCEG score recompute
  18. 2026-09-26 00:28 UTCEPSS rescore
  19. 2026-09-24 16:39 UTCEG score recompute
  20. 2026-09-24 14:04 UTCEPSS rescore
  21. 2026-09-23 18:26 UTCEG score recompute
  22. 2026-09-23 17:54 UTCEPSS rescore
  23. 2026-09-22 20:33 UTCEG score recompute
  24. 2026-09-22 19:24 UTCEG score recompute
  25. 2026-09-22 18:53 UTCEG score recompute
Show 1 more
  1. 2026-09-22 18:53 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-77256?
CVE-2026-77256 is a medium vulnerability published on September 22, 2026. MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other…
When was CVE-2026-77256 disclosed?
CVE-2026-77256 was first published on September 22, 2026, with the most recent update on September 28, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-77256 actively exploited?
CVE-2026-77256 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (25th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-77256?
CVE-2026-77256 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-77256?
A fix for CVE-2026-77256 is available: update to the fixed version the vendor names in its advisory.

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