CVE-2026-20719 — DoS via URL Previews Rendering Malicious SVGs

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HIGH

DoS via URL Previews Rendering Malicious SVGs

Published Mar 25, 2026

7.5

HIGH

CVSS 3.1

EPSS 0.35%

Description

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

Affected products

Vendor Mattermost Product Mattermost Default
unaffected
- Version
  10.11.0
  Status
  affected
  Constraints
  <=10.11.11
- Version
  11.2.0
  Status
  affected
  Constraints
  <=11.2.3
- Version
  11.3.0
  Status
  affected
  Constraints
  <=11.3.1
- Version
  11.4.0
  Status
  affected
  Constraints
  <=11.4.0
- Version
  10.11.12
  Status
  unaffected
  Constraints
  -
- Version
  11.2.4
  Status
  unaffected
  Constraints
  -
- Version
  11.3.2
  Status
  unaffected
  Constraints
  -
- Version
  11.4.1
  Status
  unaffected
  Constraints
  -
- Version
  11.5.0
  Status
  unaffected
  Constraints
  -

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor

Product

Default status

Versions

Mattermost

unaffected

Version	Status	Constraints
10.11.0	affected	<=10.11.11
11.2.0	affected	<=11.2.3
11.3.0	affected	<=11.3.1
11.4.0	affected	<=11.4.0
10.11.12	unaffected	-
11.2.4	unaffected	-
11.3.2	unaffected	-
11.4.1	unaffected	-
11.5.0	unaffected	-

github.com/mattermost/mattermost/server/v8

Go

Introduced 8.0.0-20260105080200-d27a2195068d Fixed 8.0.0-20260217110922-b7d4a1f1f59b
github.com/mattermost/mattermost-server

Go

Introduced 10.11.0-rc1+incompatible Fixed 10.11.2+incompatible
github.com/mattermost/mattermost-server

Go

Introduced 11.2.0-rc1+incompatible Fixed 11.2.4+incompatible
github.com/mattermost/mattermost-server

Go

Introduced 11.3.0-rc1+incompatible Fixed 11.3.2+incompatible
github.com/mattermost/mattermost-server

Go

Introduced 11.4.0-rc1+incompatible Fixed 11.4.1+incompatible
github.com/mattermost/mattermost-server/v5

Go

Introduced 0 Fixed not fixed
github.com/mattermost/mattermost-server/v6

Go

Introduced 0 Fixed not fixed

Ecosystem	Package	Introduced	Fixed
Go	github.com/mattermost/mattermost/server/v8	8.0.0-20260105080200-d27a2195068d	8.0.0-20260217110922-b7d4a1f1f59b
Go	github.com/mattermost/mattermost-server	10.11.0-rc1+incompatible	10.11.2+incompatible
Go	github.com/mattermost/mattermost-server	11.2.0-rc1+incompatible	11.2.4+incompatible
Go	github.com/mattermost/mattermost-server	11.3.0-rc1+incompatible	11.3.2+incompatible
Go	github.com/mattermost/mattermost-server	11.4.0-rc1+incompatible	11.4.1+incompatible
Go	github.com/mattermost/mattermost-server/v5	0	not fixed
Go	github.com/mattermost/mattermost-server/v6	0	not fixed

Remediation

Vendor solution

Update Mattermost to versions 11.5.0, 11.4.1, 11.3.2, 11.2.4, 10.11.12 or higher.

Metrics

0.35% 0.00351

Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.

EPSS probability 0.00351

Score over time

Mar–Oct 2026

EPSS v4
EPSS v5

Percentile over time

EPSS v4
EPSS v5

Table of values (3 key points)

Flat stretches are collapsed; showing up to 120 newest points.

Date	Score	Percentile	Model
Oct 1, 2026	0.35% (0.00351)	26.42th	v5 (v2026.06.15)
Jun 15, 2026	0.35% (0.00351)	26.78th	v5 (v2026.06.15)
Mar 26, 2026	0.04% (0.00039)	11.72th	v4 (v2025.03.14)

Weaknesses (1)

CWE-754

References (3)

https://github.com/advisories/GHSA-86vc-mg26-fj6x
Advisory
https://mattermost.com/security-updates
vendor-advisoryVendor Advisory
https://nvd.nist.gov/vuln/detail/CVE-2026-20719

Link	Providers	Tags
https://github.com/advisories/GHSA-86vc-mg26-fj6x		Advisory
https://mattermost.com/security-updates		vendor-advisoryVendor Advisory
https://nvd.nist.gov/vuln/detail/CVE-2026-20719