Mattermost Server vulnerable to Denial of Service through `@` character prefix inserted into JavaScript field names

published 2020-06-19 6 y ago modified 2026-06-17 4 mo ago also GHSA-jc6w-8r7f-vmp5 , GO-2025-4184 , EUVD-2017-9961

cvss: 7.5; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.1%; EPSS 1.1% chance of exploitation in 30 days, percentile 66%
public exploits: 0; none known

An issue was discovered in Mattermost Server before 4.5.0, 4.4.5, 4.3.4, and 4.2.2. It allows attackers to cause a denial of service (application crash) via an @ character before a JavaScript field name.

Patch / fix

fixed in 2 distros 2

go github.com/mattermost/mattermost-server 4.2.2, 4.2.2+incompatible, 4.3.4, 4.3.4+incompatible, 4.4.5, 4.4.5+incompatible, 4.5.0, 4.5.0+incompatible
mattermost mattermost_server 4.2.2, 4.3.4, 4.4.5

suse opensuse

govulncheck-vulndb SLE Module for Package Hub 15 SP6, openSUSE Leap 15.6 0.0.20251209T172047-150000.1.127.1

suse advisories SUSE-SU-2025:4395-1

govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Exploit prediction

1.12% chance of exploitation in the next 30 days, higher than 66% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD	2.0	5.0	AV:N/AC:L/Au:N/C:N/I:N/A:P
GitHub	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem	package	affected	fixed in
go	github.com/mattermost/mattermost-server	<4.2.2 >=4.3.0-rc1, <4.3.4 >=4.4.0-rc1, <4.4.5 >=4.5.0-rc1, <4.5.0 <4.2.2+incompatible >=4.3.0-rc1+incompatible, <4.3.4+incompatible >=4.4.0-rc1+incompatible, <4.4.5+incompatible >=4.5.0-rc1+incompatible, <4.5.0+incompatible	4.2.2 4.3.4 4.4.5 4.5.0 4.2.2+incompatible 4.3.4+incompatible 4.4.5+incompatible 4.5.0+incompatible

Classification

Weakness

CWE-248 Uncaught Exception

References

mattermost.com /security-updates/
vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2017-18871
advisory
github.com /mattermost/mattermost
package
mattermost.com /security-updates
web
github.com /advisories/GHSA-jc6w-8r7f-vmp5
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