Is CVE-2026-4858 actively exploited?

No active exploitation of CVE-2026-4858 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-4858 be exploited remotely?

Yes. CVE-2026-4858 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-4858?

CVE-2026-4858 has a CVSS score of 9.9 (CRITICAL).

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CRITICAL

CVE-2026-4858

CWE-22Published: May 21, 2026· Updated: May 21, 2026

9.9

CVSS v3.1

EPSS:0.04%probability of exploitation in 30 daysPercentile:13.9th

Official Description

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 check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action URL.. Mattermost Advisory ID: MMSA-2026-00640

NVD Source

Risk Analysis

This critical vulnerability in Mattermost allows an authenticated user to bypass security checks in integration URLs, leading to path traversal. This enables the malicious user to call arbitrary APIs using a system admin Mattermost authentication token. The CVSS score of 9.9 indicates a severe risk, as successful exploitation could lead to full compromise of confidentiality, integrity, and availability.

No public exploit is currently known for this vulnerability. However, the attack vector is network-based with low complexity, making it remotely exploitable by an authenticated user.

Recommended Action

Administrators should upgrade Mattermost to a version beyond 11.6.0, 11.5.3, 11.4.4, or 10.11.14 to address the path traversal vulnerability. Ensure all Mattermost instances are kept up-to-date with the latest security patches.

Generated by the CTIWATCH analysis pipeline from this CVE's metadata (CVSS, EPSS, KEV status, exploit intelligence). Verify against vendor advisories before acting.

Technical Analysis

CVE-2026-4858 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.9.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.