Medium severity · published Sep 14, 2026
CVE-2026-15814
Uploading a crafted image causes excessive memory allocation in the Mattermost Server
6.5
CVSS
0.4%
EPSS
No
On KEV
Description
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 limit the amount of memory allocated when decoding uploaded image files which allows an authenticated user to cause excessive server memory consumption and potential denial of service via uploading a specially crafted image as a profile picture, channel file attachment, team icon, or custom brand image. Mattermost Advisory ID: MMSA-2026-00719
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 36% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.9.0 through 11.9.0; 11.8.0 through 11.8.4; 11.7.0 through 11.7.7; 10.11.0 through 10.11.22 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.23; 11.7.0 before 11.7.8; 11.8.0 before 11.8.5; 11.9.0 before 11.9.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-15814
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-15814
Vendor Advisory
https://mattermost.com/security-updates
More from Mattermost
9.9
CVE-2026-4858
Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.
9.6
CVE-2024-39777
Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5 and 9.8.x <= 9.8.1 fail to disallow unsolicited invites to expose access to local channels, when shared channels…
9.3
CVE-2026-12985
Mattermost DCR redirect URI allowlist bypass via improper URL component validation
9.1
CVE-2023-2193
Mattermost fails to invalidate existing authorization codes when deauthorizing an OAuth2 app, allowing an attacker possessing an authorization code to generate an access token
9.1
CVE-2019-20851
An issue was discovered in Mattermost Mobile Apps before 1.26.0