4.3

CVE-2026-19603: mattermost

CVSS: 4.3v3.1MediumAwaiting analysis
Published 16-10-2026Last modified 16-10-2026
Open JSON

Vulnerability summary

CVE-2026-19603 is a medium (CVSS 4.3) vulnerability in mattermost. EPSS estimates a 0.18% chance of exploitation in the next 30 days, higher than 6.7% of scored vulnerabilities.

Overall risk
17/100
0100
Low · default modelHow is this calculated?
CVSS score
4.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.18%
0%100%
Low · Change unavailable
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 16-10-2026
    PublishedVulnerability first disclosed.
  2. 16-10-2026
    Last modifiedVulnerability information updated.

Description

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 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765

CVSS metrics

2 scores · 2 sources · 1 version

EPSS trend

Probability

0.18%

Chance of exploitation in the next 30 days

Percentile

7%

Versus all other CVEs

30-day change

Change unavailable

Change unavailable

16-10-202620-10-2026
EPSS score
0.18%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Mattermost1 product
  • mattermost≥ 11.9.0, ≤ 11.9.1 | ≥ 11.8.0, ≤ 11.8.5 | ≥ 11.7.0, ≤ 11.7.10 | ≥ 11.10.0, ≤ 11.10.1

1 vendor · 1 product

References

1 links