CVE-2026-4858
Path traversal in Mattermost integration action URL enables authenticated admin to call arbitrary API.
Is CVE-2026-4858 being exploited?
Not confirmed. CVE-2026-4858 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.33% probability of exploitation in the next 30 days.
How severe is CVE-2026-4858?
CVE-2026-4858 is rated High with a CVSS score of 8.0. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-4858?
Yes. A fix has been recorded for CVE-2026-4858. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4858 affect?
CVE-2026-4858 affects Mattermost 11.6.x <=11.6.0, Mattermost 11.5.x <=11.5.3, Mattermost 11.4.x <=11.4.4, Mattermost 10.11.x <=10.11.14. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4858?
Upgrade to patched Mattermost release when available
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Authenticated admin can call arbitrary Mattermost API endpoints via path traversal using the system token, risking data exposure or admin actions.
Patch when possible
- affected<= 11.6.0
- affected>= 11.5.0 and <= 11.5.3
- affected>= 11.4.0 and <= 11.4.4
- affected>= 10.11.0 and <= 10.11.14
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.