GHSA-jc6w-8r7f-vmp5 CVE-2017-18871 GO-2025-4184

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

High Go

Severity: 7.5 / 10; High · CVSS 3.1
Exploit chance (EPSS): 1.12%; Chance of exploitation in the next 30 days. Higher than 66.26% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-248 Uncaught Exception
Fix: 4.2.2; Upgrade github.com/mattermost/mattermost-server to this version or later

Description

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.

Affected versions

Go

Package	Vulnerable	Fixed in
github.com/mattermost/mattermost-server	`< 4.2.2`	`4.2.2`
github.com/mattermost/mattermost-server	`>= 4.3.0-rc1, < 4.3.4`	`4.3.4`
github.com/mattermost/mattermost-server	`>= 4.4.0-rc1, < 4.4.5`	`4.4.5`
github.com/mattermost/mattermost-server	`>= 4.5.0-rc1, < 4.5.0`	`4.5.0`
github.com/mattermost/mattermost-server	`< 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+incompatible` `4.3.4+incompatible` `4.4.5+incompatible` `4.5.0+incompatible`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

github.com/mattermost/mattermost-server Go → `4.2.2`

go

go get github.com/mattermost/mattermost-server@v4.2.2 && go mod tidy

Severity breakdown

CVSS 3.1 7.5

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

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-248: Uncaught Exception

An exception is thrown from a function, but it is not caught.

References

Advisories

Packages

github.com/mattermost/mattermost

Timeline

May 24, 2022 Published
Mar 3, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-xmfh-3ccg-c9fx Mattermost has an Incorrect Authorization issue	Low	Also affects github.com/mattermost/mattermost-server
GHSA-h998-hxxj-8q83 Mattermost doesn't invalidate cached authentication state for active WebSocket connections during global session revocation	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-g5vr-6pgg-74qv Mattermost doesn't enforce bot-specific permission checks on the user active status endpoint	Low	Also affects github.com/mattermost/mattermost-server
GHSA-jqgv-39mg-7c2r Mattermost doesn't authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-mxq2-5jpg-7474 Mattermost doesn't validate channel ownership of an existing subscription before applying edits	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-2g8v-grq3-hq2g Mattermost doesn't enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-6hxm-w4hv-vgvw Mattermost doesn't require role-management authorization when setting the scheme_admin flag on group syncable link and patch endpoints	High	Also affects github.com/mattermost/mattermost-server
GHSA-9p44-r552-4wp9 Mattermost doesn't sanitize the Remote Cluster API response on PATCH operations	Medium	Also affects github.com/mattermost/mattermost-server

Is this in your code?

MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.

Check your repos with MergeHarbor