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TI-2026-75211 Aliases CVE-2026-16251GHSA-9vq4-jrpg-w3w2

Mattermost image proxy buffers unbounded responses, exhausting memory

Priority LOW 29CWE-770Published · 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-770.

Summary

Mattermost 11.10.0, 11.7.0 through 11.7.9, 11.9.0 through 11.9.1 and 11.8.0 through 11.8.5 are affected. The local image proxy does not limit the size of remote image responses it buffers in memory during direct fetches, a missing limit tracked as CWE-770. A remote attacker with low privileges can exhaust server memory by supplying a crafted oversized image response, which degrades availability.

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

Description from the CNA

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to limit the size of remote image responses buffered in memory during local image proxy direct fetches, which allows a remote attacker to cause memory exhaustion on the server via a crafted oversized image response.. Mattermost Advisory ID: MMSA-2026-00726

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00286 21st percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.11.0, 11.10.1, 11.7.10 +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
MattermostMattermost11.10.0 – 11.10.0; 11.7.0 – 11.7.9; 11.9.0 – 11.9.1; 11.8.0 – 11.8.511.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6Patch availableCNA
  • Mattermost VendorMattermost Affected 11.10.0 – 11.10.0; 11.7.0 – 11.7.9; 11.9.0 – 11.9.1; 11.8.0 – 11.8.5 Fixed in 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6 Patch available CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*11.7.0 to before 11.7.10; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2VulnerableMattermost
cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:*11.10.0VulnerableMattermost
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 11.7.0 to before 11.7.10; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2 Vulnerable ·Mattermost
  • cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:* Versions 11.10.0 Vulnerable ·Mattermost

Remediation

Upgrade Mattermost to 11.11.0, 11.10.1, 11.7.10, 11.9.2 or 11.8.6, matching the release line in use. The fix is described in Mattermost advisory MMSA-2026-00726.

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

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6

Timeline

  1. 2026-10-16 Threatist record created from CVE-2026-16251
  2. 2026-10-16 Alias added: GHSA-9vq4-jrpg-w3w2

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