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Medium, CVSS 4.3

Mattermost Server allows users with a session ID to revoke another users' session

CVE-2017-18878GHSA-h564-6gc2-fcc6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/mattermost/mattermost-server 4.3.0, 4.2.1-0.20171004192657-8fbbd688ea24, 4.1.2-0.20171004201910-6be8113eb60c), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Go github.com/mattermost/mattermost-server

    Affected
    < 4.1.2-0.20171004201910-6be8113eb60c>= 4.2.0-rc1, < 4.2.1-0.20171004192657-8fbbd688ea24>= 4.3.0-rc1, < 4.3.0
    Fixed in
    4.2.1-0.20171004192657-8fbbd688ea24, 4.3.0, 4.1.2-0.20171004201910-6be8113eb60c

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
4.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
EPSS
  • CVE-2017-18878: 0.78% estimated exploitation activity in the next 30 days; percentile 55.86 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. Knowledge of a session ID allows revoking another user's session.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-h564-6gc2-fcc6

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2017-18878

Advisory: Mattermost Server allows users with a session ID to revoke another users' session
IDs: CVE-2017-18878, GHSA-h564-6gc2-fcc6
Record: https://patchnext.com/advisories/cve-2017-18878 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/mattermost/mattermost-server 4.3.0, 4.2.1-0.20171004192657-8fbbd688ea24, 4.1.2-0.20171004201910-6be8113eb60c. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost-server: affected < 4.1.2-0.20171004201910-6be8113eb60c; >= 4.2.0-rc1, < 4.2.1-0.20171004192657-8fbbd688ea24; >= 4.3.0-rc1, < 4.3.0; fixed in 4.2.1-0.20171004192657-8fbbd688ea24, 4.3.0, 4.1.2-0.20171004201910-6be8113eb60c

## Suggested inspection (read-only)
- Go github.com/mattermost/mattermost-server: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/mattermost/mattermost-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-h564-6gc2-fcc6 (GitHub-reviewed advisory GHSA-h564-6gc2-fcc6 lists affected ranges: Go github.com/mattermost/mattermost-server >=0 =4.2.0-rc1 =4.3.0-rc1 <4.3.0)

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