CVE-2026-10556

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreHIGH confidence

Score 5.3 from GitHub Security Advisory published 2026-09-14. a secondary CVSS source baseline 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate null entries in Microsoft Graph webhook notification payloads, which allows an unauthenticated attacker to crash the Microsoft Calendar plugin process and deny calendar integration service to all users on the instance via a crafted {{POST}} request to the public webhook endpoint.. Mattermost Advisory ID: MMSA-2026-00693

CVSS v3
5.3
EG Score
5.3(high)
EG Risk
39(Track)
EG Risk 39/100SSVC: Track

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
Severity53% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
16%
KEV
Not listed

Published

September 14, 2026

Last Modified

September 16, 2026

Advisory Details (1)

Auto-updated Sep 14, 2026
No patch confirmed yet.
generic

Security Updates

https://mattermost.com/security-updates

Vendor Advisories for CVE-2026-10556(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 15× in last 7d / 15× 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. 2026-09-19 00:21 UTCEG score recompute
  2. 2026-09-19 00:21 UTCGHSA enrichment
  3. 2026-09-18 19:27 UTCEPSS rescore
  4. 2026-09-17 21:59 UTCEG score recompute
  5. 2026-09-17 21:59 UTCGHSA enrichment
  6. 2026-09-16 19:36 UTCGHSA enrichment
  7. 2026-09-16 17:57 UTCEG score recompute
  8. 2026-09-16 17:57 UTCGHSA enrichment
  9. 2026-09-16 05:14 UTCEPSS rescore
  10. 2026-09-15 14:49 UTCEG score recompute
  11. 2026-09-15 14:49 UTCGHSA enrichment
  12. 2026-09-14 12:26 UTCEG score recompute
  13. 2026-09-14 11:21 UTCEG score recompute
  14. 2026-09-14 10:55 UTCEG score recompute
  15. 2026-09-14 10:54 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-10556?
CVE-2026-10556 is a medium vulnerability published on September 14, 2026. Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate null entries in Microsoft Graph webhook notification payloads, which allows an unauthenticated attacker to crash the Microsoft Calendar plugin process and deny calendar integration service…
When was CVE-2026-10556 disclosed?
CVE-2026-10556 was first published in the National Vulnerability Database on September 14, 2026, with the most recent update on September 16, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-10556 actively exploited?
CVE-2026-10556 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 83.5% of all scored CVEs.
What is the CVSS score of CVE-2026-10556?
CVE-2026-10556 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-10556?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-10556, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-10556

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