DoS via URL Previews Rendering Malicious SVGs

published 2026-03-25 7 mo ago modified 2026-06-25 4 mo ago also GHSA-86vc-mg26-fj6x , GO-2026-5245 , EUVD-2026-15485

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 29%
public exploits: 0; none known

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

Patch / fix

fixed in 3 distros 1

go github.com/mattermost/mattermost/server/v8 8.0.0-20260217110922-b7d4a1f1f59b, 10.11.2, 11.2.4, 11.3.2, 11.4.1
go github.com/mattermost/mattermost-server 10.11.2+incompatible, 11.2.4+incompatible, 11.3.2+incompatible, 11.4.1+incompatible
Mattermost Mattermost 10.11.12, 11.2.4, 11.3.2, 11.4.1, 11.5.0

govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-26)

Exploit prediction

0.36% chance of exploitation in the next 30 days, higher than 29% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
NVD	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem	package	affected	fixed in
go	github.com/mattermost/mattermost/server/v8	>=11.4.0-rc1, <11.4.1 >=11.3.0-rc1, <11.3.2 >=11.2.0-rc1, <11.2.4 >=8.0.0-20260105080200-d27a2195068d, <8.0.0-20260217110922-b7d4a1f1f59b >=10.11.0-rc1, <10.11.2	11.4.1 11.3.2 11.2.4 8.0.0-20260217110922-b7d4a1f1f59b 10.11.2
go	github.com/mattermost/mattermost-server	>=10.11.0-rc1+incompatible, <10.11.2+incompatible >=11.2.0-rc1+incompatible, <11.2.4+incompatible >=11.3.0-rc1+incompatible, <11.3.2+incompatible >=11.4.0-rc1+incompatible, <11.4.1+incompatible	10.11.2+incompatible 11.2.4+incompatible 11.3.2+incompatible 11.4.1+incompatible
go	github.com/mattermost/mattermost-server/v5	all versions	no fix listed
go	github.com/mattermost/mattermost-server/v6	all versions	no fix listed

Affected products

Mattermost Mattermost

Classification

Weakness

CWE-754 Improper Check for Unusual or Exceptional Conditions

References

mattermost.com /security-updates
vendor-advisory, web
nvd.nist.gov /vuln/detail/CVE-2026-20719
advisory
github.com /mattermost/mattermost
package
github.com /advisories/GHSA-86vc-mg26-fj6x
advisory

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary