CVE-2026-18795· CVE.org (no NVD analysis yet)· CNA Mattermost

Missing server side validation allowed user to quarantine a DM and GM post

Noroxi assessment

Priority: Monitor (action score 25/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.15% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. Special conditions such as timing or configuration are required.
According to the record, no fixed version is available yet.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756

MediumCVSS 6.4 · v3.1—No exploit No fix recorded

Broken access control (IDOR)

EUVD-2026-102813

Published: Oct 16, 2026
Updated: Oct 16, 2026
EPSS: 0.1% · 3th percentile
CWE: CWE-862

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Action score

Monitor

Low priority for now.

CVSS: 25 / 40 · 6.4 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.1%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · Mattermost: 6.4; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

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Versions reported by the vendor

Affected version ranges reported by the assigning authority (Mattermost). Independent of NVD's CPE analysis and usually ahead of it.

Mattermost Mattermost
- 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6not affected
- 11.10.0 and later · up to and including 11.10.0affected · semver
- 11.7.0 and later · up to and including 11.7.9affected · semver
- 11.9.0 and later · up to and including 11.9.1affected · semver
- 11.8.0 and later · up to and including 11.8.5affected · semver

Same product

mattermost: all records

Other highest-scoring records for the same primary product.

CVE-2024-39777Malicious remote can invite itself to an arbitrary local channel
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CVE-2023-2193Oauth authorization codes do not expire when deauthorizing an oauth2 app
36Monitor
CVE-2019-20851An issue was discovered in Mattermost Mobile Apps before 1.26.0.
36Monitor

Published before and after this one in the same product

← EarlierCVE-2026-16049Aug 17, 2026 · _GitLab Plugin allows cross-channel post injection and phishing via missing channel permission checks in issue API endpoints_
17Monitor
← EarlierCVE-2026-18551Oct 16, 2026 · Mattermost guest account privilege escalation via member roles API
26Monitor
Later →CVE-2026-19541Oct 16, 2026 · Outgoing OAuth connection client secret exposure during connection validation
26Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Harshil Sharmafinder

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-187990 days apartMattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users
17Monitor
CVE-2026-1604960 days apart_GitLab Plugin allows cross-channel post injection and phishing via missing channel permission checks in issue API endpoints_
17Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope