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Fencer Vulns
medium 6.5

CVE-2026-4915 json

Server panic via outgoing webhook responses

published 2026-05-25 5 mo ago modified 2026-07-23 3 mo ago also GHSA-5gmf-x7hg-97wf , GO-2026-5845 , EUVD-2026-31646

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 20%
public exploits
0
none known

Summary

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641

Patch / fix

  • go github.com/mattermost/mattermost-server 10.11.15, 10.11.15+incompatible, 11.4.5, 11.4.5+incompatible, 11.5.4, 11.5.4+incompatible, 11.6.1, 11.6.1+incompatible
  • go github.com/mattermost/mattermost/server/v8 8.0.0-20260407102538-faa7d75b4ea0
  • Mattermost Mattermost 10.11.15, 11.4.5, 11.5.4, 11.6.1, 11.7.0
  • 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
5 mo ago

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
go github.com/mattermost/mattermost-server
>=11.6.0, <11.6.1
>=11.5.0, <11.5.4
>=11.4.0, <11.4.5
>=10.11.0, <10.11.15
>=10.11.0+incompatible, <10.11.15+incompatible
>=11.4.0+incompatible, <11.4.5+incompatible
>=11.5.0+incompatible, <11.5.4+incompatible
>=11.6.0+incompatible, <11.6.1+incompatible
11.6.1
11.5.4
11.4.5
10.11.15
10.11.15+incompatible
11.4.5+incompatible
11.5.4+incompatible
11.6.1+incompatible
go github.com/mattermost/mattermost/server/v8
<8.0.0-20260407102538-faa7d75b4ea0
8.0.0-20260407102538-faa7d75b4ea0
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

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.