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CVE-2026-86348— MS Calendar plugin: unrecovered handler panics from malformed post-action requests could crash the plugin process

Quick assessment

Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mattermost 版本 ≤ 11.9.11.0.9、11.4.8、11.7.7、10.22.11.0.0 无法从处理程序的 panic（异常中断）中恢复，这使得经过身份验证的用户能够通过携带意外字段类型的 post-action（帖子操作）请求使插件崩溃。Mattermost 公告 ID：MMSA-2026-00701

CVSS 4.3 · Medium
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I. Basic Information for CVE-2026-86348

Vulnerability Information
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Vulnerability Title
MS Calendar plugin: unrecovered handler panics from malformed post-action requests could crash the plugin process
Source: CVE Program / CVE List V5
Vulnerability 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
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
不正确的类型转换
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mattermost Mattermost <=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 -

II. Public POCs for CVE-2026-86348

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III. Intelligence Information for CVE-2026-86348

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Same Patch Batch · Mattermost · 2026-09-14 · 15 CVEs total

CVE-2026-8821 7.1 HIGH Playbooks run owner channel membership permission bypass
CVE-2026-12985 6.8 MEDIUM Mattermost DCR redirect URI allowlist bypass via improper URL component validation
CVE-2026-9812 6.5 MEDIUM Missing property field ownership validation in Playbooks run property update endpoint
CVE-2026-5132 6.5 MEDIUM Unbounded zlib decompression in Calls SDP WebSocket messages
CVE-2026-15814 6.5 MEDIUM Uploading a crafted image causes excessive memory allocation in the Mattermost Server
CVE-2026-82920 5.5 MEDIUM Mattermost ABAC parent policy bypass via policy update endpoint
CVE-2026-10556 5.3 MEDIUM Unauthenticated webhook request with null notification entry could crash the Microsoft Cal
CVE-2026-10542 5.0 MEDIUM Playbooks channel action update validation issue
CVE-2026-86349 4.3 MEDIUM Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting
CVE-2026-13417 4.3 MEDIUM Boards plugin denial of service via unvalidated block fields.properties
CVE-2026-14344 4.3 MEDIUM Inconsistent authorization checks in Mattermost Boards endpoints
CVE-2026-12882 4.3 MEDIUM Mattermost Markdown autolink parsing denial of service
CVE-2026-11993 4.3 MEDIUM Fix authenticated members disabling file content indexing server-wide via extraction pool
CVE-2026-14259 4.3 MEDIUM Board archive import bypasses team board creation permissions

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-704

V. Comments for CVE-2026-86348

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