CVE-2026-86348

MS Calendar plugin: unrecovered handler panics from malformed post-action requests could crash the plugin process

MEDIUM

4.3

CVSS Score

Published: September 14, 2026 at 01:52 PM UTC

Updated: October 14, 2026 at 07:28 PM UTC

2 products affected across 1 vendorMattermost ServerMattermost

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Severity

MEDIUM4.3

Exploit prediction

EPSS 0.4%

SSVC

No known exploit

Description

Mattermost versions <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 fail to recover from handler panics, which allows an authenticated user to crash the plugin via a post-action request with an unexpected field type.. Mattermost Advisory ID: MMSA-2026-00701

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mattermost Server · Mattermost

95%

10.11.0 ≤ v < 10.11.2311.7.0 ≤ v < 11.7.811.8.0 ≤ v < 11.8.511.9.0 ≤ v < 11.9.1

Mattermost · Mattermost

90%

v ≤ <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0<=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0

Vendor states this is fixed in 10.11.23 (unaffected)

Vendor states this is fixed in 11.10.0 (unaffected)

Vendor states this is fixed in 11.7.8 (unaffected)

Vendor states this is fixed in 11.8.5 (unaffected)

Vendor states this is fixed in 11.9.1 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://mattermost.com/security-updates

References (1)

Vendor Advisory

Source: cverecord

https://mattermost.com/security-updates

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

4.3MEDIUMMattermost

Attack Vector: NETWORK
Complexity: LOW
Privileges: LOW
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: NONE
Integrity: NONE
Availability: LOW

Vector?

Quick Info

StatusANALYZED

CWE

CWE-704

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