Information Disclosure via WebSocket Event When Deleting Unrevealed Burn on Read Posts

published 2026-03-16 7 mo ago modified 2026-06-17 4 mo ago also GHSA-3rhr-jr63-hwq5 , GO-2026-4734 , EUVD-2026-12415

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits: 0; none known

Mattermost versions 11.3.x <= 11.3.0 fail to preserve the redacted state of burn-on-read posts during deletion which allows channel members to access unrevealed burn-on-read message contents via the WebSocket post deletion event.. Mattermost Advisory ID: MMSA-2026-00579

Patch / fix

fixed in 3 distros 2 links 1

go github.com/mattermost/mattermost/server/v8 8.0.0-20260127062706-c6b205f0d770
go github.com/mattermost/mattermost-server 5.3.2-0.20260127062706-c6b205f0d770, 10.11.11, 10.11.11+incompatible, 11.2.3, 11.2.3+incompatible, 11.3.1, 11.3.1+incompatible
Mattermost Mattermost 11.3.1, 11.4.0

suse opensuse

govulncheck-vulndb openSUSE Leap 15.6 0.0.20260326T203309-150000.1.155.2

suse advisories SUSE-SU-2026:1135-1

govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

github.com/mattermost/mattermost@c6b205f commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-16)

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 14% 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:L/I:N/A:N
GitHub	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Affected packages

ecosystem	package	affected	fixed in
go	github.com/mattermost/mattermost/server/v8	<8.0.0-20260127062706-c6b205f0d770	8.0.0-20260127062706-c6b205f0d770
go	github.com/mattermost/mattermost-server	<5.3.2-0.20260127062706-c6b205f0d770 >=10.11.0-rc1, <10.11.11 >=11.2.0-rc1, <11.2.3 >=11.3.0-rc1, <11.3.1 >=10.11.0-rc1+incompatible, <10.11.11+incompatible >=11.2.0-rc1+incompatible, <11.2.3+incompatible >=11.3.0-rc1+incompatible, <11.3.1+incompatible	5.3.2-0.20260127062706-c6b205f0d770 10.11.11 11.2.3 11.3.1 10.11.11+incompatible 11.2.3+incompatible 11.3.1+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-201 Insertion of Sensitive Information Into Sent Data

References

github.com /mattermost/mattermost/commit/c6b205f0d77080ef805783de0628b9526af7faec
web
mattermost.com /security-updates
vendor-advisory, web
nvd.nist.gov /vuln/detail/CVE-2026-2578
advisory
github.com /mattermost/mattermost
package
github.com /advisories/GHSA-3rhr-jr63-hwq5
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