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CVE-2026-20719· NVD / CVE Program· CNA Mattermost

DoS via URL Previews Rendering Malicious SVGs

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID: MMSA-2026-00595

HighCVSS 7.5 · v3.1—No exploit Fix available
Published
Mar 25, 2026
Updated
Jun 17, 2026
EPSS
0.4% · 26th percentile
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Report tools

JSON

Action score

30

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
7.5
CNA · Mattermost
4.3
3.2 point gap

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

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

Affected systems

VendorProduct
mattermostmattermost server

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • mattermost mattermost server10.11.0 and later · before 10.11.12
  • mattermost mattermost server11.2.0 and later · before 11.2.4
  • mattermost mattermost server11.3.0 and later · before 11.3.2
  • mattermost mattermost server11.4.0 and later · before 11.4.1

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

    • 11.5.0, 11.4.1, 11.3.2, 11.2.4, 10.11.12not affected
    • 11.4.0 and later · up to and including 11.4.0affected · semver
    • 11.3.0 and later · up to and including 11.3.1affected · semver
    • 11.2.0 and later · up to and including 11.2.3affected · semver
    • 10.11.0 and later · up to and including 10.11.11affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Gogithub.com/mattermost/mattermost-serverfrom 10.11.0-rc1+incompatible · before 10.11.2+incompatible10.11.2+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.2.0-rc1+incompatible · before 11.2.4+incompatible11.2.4+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.3.0-rc1+incompatible · before 11.3.2+incompatible11.3.2+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.4.0-rc1+incompatible · before 11.4.1+incompatible11.4.1+incompatible
Gogithub.com/mattermost/mattermost-server/v5all versions—
Gogithub.com/mattermost/mattermost-server/v6all versions—
Gogithub.com/mattermost/mattermost/server/v8from 10.11.0-rc1 · before 10.11.210.11.2
Gogithub.com/mattermost/mattermost/server/v8from 11.2.0-rc1 · before 11.2.411.2.4
Gogithub.com/mattermost/mattermost/server/v8from 11.3.0-rc1 · before 11.3.211.3.2
Gogithub.com/mattermost/mattermost/server/v8from 11.4.0-rc1 · before 11.4.111.4.1
Gogithub.com/mattermost/mattermost/server/v8from 8.0.0-20260105080200-d27a2195068d · before 8.0.0-20260217110922-b7d4a1f1f59b8.0.0-20260217110922-b7d4a1f1f59b

Same product

mattermost: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-4858Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.
    39Monitor
  • CVE-2025-12421Account Takeover via Code Exchange Endpoint
    39Monitor
  • CVE-2025-12419Account takeover on OAuth/OpenID-enabled servers
    39Monitor
  • CVE-2025-4981Path Traversal Leading to RCE by Any Authenticated Mattermost User
    39Monitor
  • CVE-2023-6458Client side path traversal due to lack of route parameters validation
    39Monitor
  • CVE-2017-18920An issue was discovered in Mattermost Server before 3.6.2.
    39Monitor

Remediation

Which version to upgrade to

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

Product / packageFixed versionSource
Go:github.com/mattermost/mattermost-server10.11.2+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.2.4+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.3.2+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.4.1+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost/server/v810.11.2Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v811.2.4Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v811.3.2Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v811.4.1Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v88.0.0-20260217110922-b7d4a1f1f59bPackage registry (OSV)

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.

Variant candidates

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

  • CVE-2026-405451 days apartSVG content served through Mattermost image proxy despite Content-Type restrictions causes client-side denial of service
    26Monitor
  • CVE-2026-491561 days apartServer panic via outgoing webhook responses
    26Monitor
  • CVE-2025-0503404 days apartLeaked User IDs and Metadata of Deleted DMs
    21Monitor
  • CVE-2025-22445440 days apartMisleading UI for undefined admin console settings in Calls causes security confusion
    21Monitor
  • CVE-2024-11599482 days apartDomain Restriction Bypass on Registration
    21Monitor
  • CVE-2026-31091 days apartMissing timestamp validation in Zoom webhook handler
    8Monitor

Chain candidates

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

—

Bug bounty scope

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-754 · Improper Check for Unusual or Exceptional Conditions

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

We use this product, ask for help

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records