VulnSocial

CVE-2026-21386Disclosure(mattermost / mattermost_server)

LOWCVSS 4.3 · MEDIUM

Signal is active with 1 mentions in latest observed window

Immediate actions

  • Patch mattermost mattermost_server systems immediately

Recommended action window: Monitor and triage in normal cycle

NVD description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588

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0.5/ 10 priority

Sources & remediation

Vendor / third-party advisories
Weakness type (CWE)
CWE-203

Priority

LOW

Exploitation

NONE

PoC

NONE

Patch

AVAILABLE

Momentum

STABLE

Are you affected?

If you run products in this scope, you should treat this CVE as relevant to your environment.

  • mattermost_server

Threat summary

  • Patch or workaround signal is available
  • 3 mentions across 2 observed days
  • Momentum state: stable

What's happening

  • Patch or workaround mentioned in 1 signal
  • Technical details provided in 3 signals
  • Disclosure: 2 classified signals
  • Peaked 1d ago at 2 mentions (2026-03-16); latest day: 1
  • 3 total mentions across 2 days

Affected systems

Vendors
mattermost
Products
mattermost_server

Deep dive

Activity timeline3 mentions / 2d
01122Mentions · 2026-03-16: 2Mentions · 2026-03-17: 1Patch / Workaround · 2026-03-17: 1Technical Details · 2026-03-16: 2Technical Details · 2026-03-17: 103-1603-17
Signal classification2 categories
Disclosure
266.7%
Patch
133.3%
Referenced assets2 URLs
Classification over time
DateTotalLabels
2026-03-162
Disclosure2
2026-03-171
Patch1
Full discourse3 posts
  • RagingCISO@CisoRaging77913
    Patch

    🔴 CVE-2026-21386: Mattermost error messages differ for nonexistent vs private channels. /mute enumeration = map all secret channels. CVSS 4.3, impact: your exec discussions. Security as afterthought to UX. Patch before someone sells your channel list.

    Post summary

    The post highlights a disclosure-based vulnerability in Mattermost, provides technical details and a CVSS score, and urges users to apply the patch before potential exploitation.

    0000041
    4 followersView on X
  • Vulmon Vulnerability Feed@VulmonFeeds
    Disclosure

    CVE-2026-21386 Information Disclosure Vulnerability in Mattermost via Channel Enumeration https://vulmon.com/vulnerabilitydetails?qid=CVE-2026-21386

    Post summary

    The text announces an information‑disclosure flaw in Mattermost (CVE‑2026‑21386) identified as a channel enumeration vulnerability, presenting basic technical details but no PoC, exploit, or patch information.

    0000060
    4.0K followersView on X
  • CVE@CVEnew
    Disclosure

    CVE-2026-21386 Mattermost versions 11.3.x &lt;= 11.3.0, 11.2.x &lt;= 11.2.2, 10.11.x &lt;= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an aut… https://www.cve.org/CVERecord?id=CVE-2026-21386

    Post summary

    The text announces CVE-2026-21386, noting a bug in certain Mattermost versions that causes inconsistent error responses when the /mute command is used, but it does not provide any PoC, exploit details, or patch information.

    0000079
    56.7K followersView on X
CPE platform detail1 entries

1 of 1 entries

PartVendorProductVersionTarget SWTarget HW
Appmattermostmattermost_server---

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