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CVE-2018-21259

19
FAUCET Score

CVE-2018-21259 is a denial-of-service vulnerability affecting Mattermost Server versions prior to 4.10.1, 4.9.4, and 4.8.2. An unauthenticated attacker can exploit this by sending a malformed link to a channel, causing the application to hang. Rated as Medium severity (CVSS 5.3), this vulnerability is easily exploitable over the network with low attack complexity, leading to a denial of service. There is no impact on confidentiality or integrity. Currently, there is no evidence of active exploitation, nor are there any public exploit modules or proof-of-concept code available. The vulnerability has received minimal community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.8.2CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
>= 4.9.0, < 4.9.4CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
>= 4.10.0, < 4.10.1CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
LOW
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.10%
Probability of exploitation in next 30 days
EPSS Percentile
62.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0110 is in the 40th percentile among its peer group of 23,725 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

mattermost.com / security-updates
Vendor Advisory