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CVE-2026-6046

Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server

CVSS 3.1 5.3 MEDIUMEUVD CVSS 3.1 5.3 CVSS 3.1 · [email protected] · Secondary 5.3 MEDIUMCVSS_V3 Publisher rating MODERATEFixed by github.com/mattermost/mattermost-server 11.6.1Fixed by github.com/mattermost/mattermost-server 11.5.5Fixed by github.com/mattermost/mattermost-server 10.11.17Fixed by github.com/mattermost/mattermost/server/v8 8.0.0-20260428151657-c79c3831061aosv · severity unknownFixed by github.com/mattermost/mattermost-server 10.11.17+incompatibleFixed by github.com/mattermost/mattermost-server 11.5.5+incompatibleFixed by github.com/mattermost/mattermost-server 11.6.1+incompatibleFixed by github.com/mattermost/mattermost/server/v8 8.0.0-20260428151657-c79c3831061aKEV status unknown
Original advisory

cve-program · CVE-2026-6046

Published

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Read the publisher's advisory

euvd · EUVD-2026-36502

Published

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Read the publisher's advisory

nvd · CVE-2026-6046

Published

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Read the publisher's advisory

osv · GHSA-3vmp-whvv-5v9v

Published

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username. Mattermost Advisory ID: MMSA-2026-00649

Read the publisher's advisory

osv · GO-2026-6279

Published

Mattermost doesn't validate that a username returned during bot registration belongs to a bot account in github.com/mattermost/mattermost-server

Read the publisher's advisory

Affected versions, risk and source history

Exploitation and risk

Source status

CISA KEV lists vulnerabilities known to be exploited. FIRST EPSS estimates the likelihood of exploitation in the next 30 days. An unavailable score does not mean zero risk.

Which CVEs have scores here?

This view includes predictions for CVE identifiers explicitly listed in public NuGet advisories. Microsoft release pages have their own prediction coverage. Check source status for the scope and latest checks.

No exploitation or prediction data is available here for these CVEs. This does not mean they are safe or unlikely to be exploited.

cve-program · CVE-2026-6046

Published

Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Source published
12 Jun 2026 15:52:33 UTC
Source modified
12 Jun 2026 17:18:30 UTC
Saved here
23 Oct 2026 15:48:27 UTC
Source terms
CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

euvd · EUVD-2026-36502

Published

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept …

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Additional publisher context

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Jun 12, 2026, 3:52:33 PM

dateUpdated: Jun 12, 2026, 5:18:30 PM

1 related source bulletins · separate from aliases

WID-SEC-W-2026-1529: Mattermost Server: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

CVE-2026-3433 · CVE-2026-6046 · CVE-2026-6689 · CVE-2026-6739 · CVE-2026-6961 · CVE-2026-7387

Source published
Jun 12, 2026, 3:52:33 PM (timezone not stated)
Source modified
Jun 12, 2026, 5:18:30 PM (timezone not stated)
Saved here
15 Nov 2026 17:54:03 UTC
Source terms
ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

nvd · CVE-2026-6046

Published

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept …

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Additional publisher context

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Analyzed

Weakness classifications: CWE-200

Original publisher date fields

published: 2026-06-12T17:16:26.957

lastModified: 2026-06-18T14:33:35.203

1 source CPE criteria · context only
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published
12 Jun 2026 17:16:26 UTC
Source modified
18 Jun 2026 14:33:35 UTC
Saved here
25 Oct 2026 14:19:22 UTC
Source terms
NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

osv · GHSA-3vmp-whvv-5v9v

Published

Mattermost doesn't validate that a username returned during bot registration belongs to a bot account

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username. Mattermost Advisory ID: MMSA-2026-00649

Source published
12 Jun 2026 18:31:59 UTC
Source modified
10 Sep 2026 03:50:55 UTC
Saved here
24 Oct 2026 13:19:41 UTC
Source terms
GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

Publisher rating · MODERATE

osv · GO-2026-6279

Published

Mattermost doesn't validate that a username returned during bot registration belongs to a bot account in github.com/mattermost/mattermost-server

Mattermost doesn't validate that a username returned during bot registration belongs to a bot account in github.com/mattermost/mattermost-server

Source published
25 Aug 2026 19:43:10 UTC
Source modified
26 Aug 2026 01:13:10 UTC
Saved here
24 Oct 2026 13:19:41 UTC
Source terms
OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · OSV · upstream source license applies. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

ChangeIntel

An IT change radar: releases, security, known issues, retirements, documentation changes, and service status from public sources. Every item links to supporting evidence; dates and statuses can change after they are read.

Sources read 15 Nov 23:13 UTC · 274 of 275 readable · 250 fully read · 18 waiting for GitHub's hourly limit · documentation 461/469 current

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