CVE-2026-3472 — Markdown image rendering bypass in AI bot tool result posts in Mattermost
Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into tool result content rendered by a victim's client.. Mattermost Advisory ID: MMSA-2026-00619
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.3% (30-day exploitation probability)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Mattermost Mattermost, Mattermost Mattermost Server).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Exploitation requires user interaction: tighten email/web filtering and warn affected users.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Mattermost | Mattermost | ≥ 10.11.0 and ≤ 10.11.18≥ 11.6.0 and ≤ 11.6.3≥ 11.5.0 and ≤ 11.5.6 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Mattermost | Mattermost Server | ≥ 10.11.0 and < 10.11.19≥ 11.5.0 and < 11.5.7≥ 11.6.0 and < 11.6.4 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 3.5 | CVSS 3.1 | Low | 2.1 | 1.4 | responsibledisclosure@mattermost.com via NIST National Vulnerability Database |
| 3.5 | CVSS 3.1 | Low | — | — | Mattermost via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N (score shown at the top: responsibledisclosure@mattermost.com) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.27%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · mattermost/mattermost
- SSVC assessment updated
- Record published
- CVSS changed · 3.5
- Source status changed · → Analyzed
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
1 on the record
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-96260 Mattermost server missing request body size limit on plugin routes allows denial of service by an authenticated user 22d
- Medium CVE-2026-96259 Mattermost server-side request forgery via OAuth endpoints configurable by a System Administrator 22d
- Medium CVE-2026-95666 Unbounded post ID array in the bulk reactions endpoint allows denial of service 23d
- Low CVE-2026-75588 Mattermost Desktop App plugin popout scheme validation bypass 28d
- Low CVE-2026-12284 Mattermost Desktop App Missing IPC Sender Validation in Calls Leave Handler 28d
- Medium CVE-2026-75025 Mattermost Desktop local network access from server-rendered content 29d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-3472 is "Markdown image rendering bypass in AI bot tool result posts in Mattermost", rated Low. It affects Mattermost (Mattermost); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 3.5 describes technical severity. EPSS 0.27% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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