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TI-2026-80426 Aliases CVE-2026-93849GHSA-w44p-jxhf-26w5

Mattermost allows excessive memory allocation via crafted WebSocket frames

Priority LOW 29CWE-789Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-789.

Summary

Mattermost versions from 11.7.0 through 11.7.10, from 11.8.0 through 11.8.5, from 11.9.0 through 11.9.1, and from 11.10.0 through 11.10.1 do not apply allocation limits to byte-string decoding in the WebSocket msgpack decoder, which is CWE-789. An authenticated remote attacker can send a crafted binary WebSocket frame that declares a very large payload length, causing excessive server memory allocation and a denial of service.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 Mattermost fail to apply allocation limits to the byte-string decode paths in its WebSocket msgpack decoder, which allows an authenticated remote attacker to cause excessive server memory allocation via a crafted binary WebSocket frame declaring a Bin32 payload length of up to 4,294,967,295 bytes.. Mattermost Advisory ID: MMSA-2026-00768

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00468 40th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.11.0, 11.9.2, 11.8.6 +2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MattermostMattermost11.9.0 – 11.9.1; 11.8.0 – 11.8.5; 11.7.0 – 11.7.10; 11.10.0 – 11.10.111.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2Patch availableCNA
  • Mattermost VendorMattermost Affected 11.9.0 – 11.9.1; 11.8.0 – 11.8.5; 11.7.0 – 11.7.10; 11.10.0 – 11.10.1 Fixed in 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*11.7.0 to before 11.7.11; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2; 11.10.0 to before 11.10.2VulnerableMattermost
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 11.7.0 to before 11.7.11; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2; 11.10.0 to before 11.10.2 Vulnerable ·Mattermost

Remediation

Upgrade Mattermost to 11.7.11, 11.8.6, 11.9.2, 11.10.2, or 11.11.0. The sources list no advisory id beyond MMSA-2026-00768.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2

Timeline

  1. 2026-10-26 Threatist record created from CVE-2026-93849
  2. 2026-10-26 CISA SSVC decision points changed
  3. 2026-10-26 Priority changed: MEDIUM → LOW
  4. 2026-10-27 Alias added: GHSA-w44p-jxhf-26w5

References

Advisory 1

  • TI-2025-18933 Arbitrary file read in Mattermost Boards via import & export board archive CVSS 3.1CRITICAL 9.9
  • TI-2025-04465 Path Traversal Leading to RCE by Any Authenticated Mattermost User CVSS 3.1CRITICAL 9.9
  • TI-2017-14068 An issue was discovered in Mattermost Server before 3.6.2. CVSS 3.1CRITICAL 9.8
  • TI-2017-14060 An issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. CVSS 3.1CRITICAL 9.8
  • TI-2017-14048 An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. CVSS 3.1CRITICAL 9.8
  • TI-2025-14360 Arbitrary file read via block duplication in Mattermost Boards CVSS 3.1CRITICAL 9.9
See all 505 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences