CVE Explorer

CVE-2026-27656

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow.. Mattermost Advisory ID: MMSA-2026-00590

Lifecycle PUBLISHED1 preserved revisionFact urn:baitaphish:canonical-cve-fact-revision:v2:5c3cc6993a8f6d05736dd7036c45d7410363aba055f333c1936367540af48964

Known exploited

Not asserted

Disputed

Stale source

Conflicts

Affected products and versions

1 source assertion

{"defaultStatus":"unaffected","product":"Mattermost","vendor":"Mattermost","versions":[{"lessThanOrEqual":"11.4.0","status":"affected","version":"11.4.0","versionType":"semver"},{"lessThanOrEqual":"11.3.1","status":"affected","version":"11.3.0","versionType":"semver"},{"lessThanOrEqual":"11.2.3","status":"affected","version":"11.2.0","versionType":"semver"},{"lessThanOrEqual":"10.11.11","status":"affected","version":"10.11.0","versionType":"semver"},{"status":"unaffected","version":"11.5.0"},{"status":"unaffected","version":"11.4.1"},{"status":"unaffected","version":"11.3.2"},{"status":"unaffe…

cve_program_cvelist_v5affected
urn:baitaphish:normalized-source-record:v2:7acfbf8c369a0765fd5d24efcc510bf33b6c6aea67d211268e203e22b485b97d · sha256:54c569131e15bba9… · /containers/cna/affected/0

Provider-owned CVSS observations

1 source assertion

{"metric":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":5.7,"baseSeverity":"MEDIUM","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"HIGH","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N","version":"3.1"},"metric_type":"cvssV3_1"}

cve_program_cvelist_v5cvss
urn:baitaphish:normalized-source-record:v2:7acfbf8c369a0765fd5d24efcc510bf33b6c6aea67d211268e203e22b485b97d · sha256:54c569131e15bba9… · /containers/cna/metrics/0/cvssV3_1

CWE assertions

1 source assertion

{"cweId":"CWE-303","description":"CWE-303: Incorrect Implementation of Authentication Algorithm","lang":"en","type":"CWE"}

cve_program_cvelist_v5cwe
urn:baitaphish:normalized-source-record:v2:7acfbf8c369a0765fd5d24efcc510bf33b6c6aea67d211268e203e22b485b97d · sha256:54c569131e15bba9… · /containers/cna/problemTypes/0/descriptions/0

Source references

1 source assertion

{"name":"MMSA-2026-00590","tags":["vendor-advisory"],"url":"https://mattermost.com/security-updates"}

cve_program_cvelist_v5reference
urn:baitaphish:normalized-source-record:v2:7acfbf8c369a0765fd5d24efcc510bf33b6c6aea67d211268e203e22b485b97d · sha256:54c569131e15bba9… · /containers/cna/references/0

Attribution and limitations

CVE Program CVEList V5: Reproduce the MITRE copyright designation and CVE license in copies. Source →

Provider severity values are preserved separately. Baitaphish does not convert them into a risk rating, infer affected products, or treat EPSS as observed exploitation.

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