What is CVE-2026-2578?

CVE-2026-2578 is a medium-severity vulnerability in Mattermost, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 4.3/10. Published 2026-03-16.

How severe is CVE-2026-2578?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Mattermost

CVE-2026-2578

Mattermost versions 11.3.x <= 11.3.0 fail to preserve the redacted state of burn-on-read posts during deletion which allows channel members to access unrevealed burn-on-read message contents via the WebSocket post deletion event.. Mattermost Advisory ID: MMSA-2026-00579

Published 2026-03-16 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.003 (20.5th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 20.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Mattermost — versions 11.3.0, 11.4.0, 11.3.1
Mattermost Server

Weakness classification (CWE)

CWE-201 — Insertion of Sensitive Information into Sent Data

References

mattermost.com/security-updates (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-2578?: CVE-2026-2578 is a medium-severity vulnerability in Mattermost, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 4.3/10. Published 2026-03-16.
How severe is CVE-2026-2578?: Medium severity. CVSS v3 base score is 4.3 out of 10.